Webinar Recap: Two-Pass Technique with MS Project

Please find below a transcription of the audio portion of Satya Narayan Dash’s session, Two-Pass Technique with MS Project, being provided by MPUG for the convenience of our members. You may wish to use this transcript for the purposes of self-paced learning, searching for specific information, and/or performing a quick review of webinar content. There may be exclusions, such as those steps included in product demonstrations. You may watch the live recording of this webinar at your convenience.

Kyle: Hello everyone, and welcome to today’s MPUG webinar, Two-Pass Technique with Microsoft Project. My name is Kyle, and I’ll be the moderator today. Today’s session is eligible for 1 PMI PDU in the technical category. The MPUG activity code for claiming that with PMI is on the screen now. And like all MPUG webinars, the recording of this session will be posted to mpug.com shortly after the live presentation ends, and all MPUG members can watch the recordings at any time and still be eligible to earn the PDU credit.

Kyle: All the sessions you watch on demand can be submitted to your webinar history, and the live sessions you attend are automatically submitted. Within your history, you can print or download your transcript, your certificates of completion, including the one for today, and you can access that by logging into mpug.com. Click the My Account button and click on the transcript link. If you have any questions during today’s presentation, please send those over at any time using the chat question box, on the Go To Webinar control panel. We do plan to answer those for you during the session today.

Kyle: All right, we’ll go ahead and get started. We’re very happy to welcome back Satya Dash today. Satya is a management professional speaker, coach and author of six books. His video courses, PMP live lessons, guaranteed pass and PMP 35 contact hours online, have created many successful PMPs. In his course of MS Project live lessons is one of the most used courses by management practitioners. Over 1500 people have successfully cracked the PMP examination with Satya’s leadership. So with that said welcome back Satya, and at this time I’ll hand it over to you to get us started with today’s discussion.

Satya Dash: Thank you, Kyle, for having me here and thank you for the introduction. Hello everyone. So today’s topic per webinar will be Two-Pass Technique with Microsoft Project. So Kyle has already given the introduction, I’m going to skip the slide, and this is what we are going to discuss, looking ahead. How to conduct forward pass and backward pass calculations. How to determine the total float for the activities. What are the significances of total float, early start, early finish, late start and late finish. How does Microsoft project software address this two-pass technique? And we’ll see how does Microsoft Project software determines the total float?

Satya Dash: So first a brief interaction. Now that many scheduling approaches, why you go for a schedule in your project or program or any other plan that you are going to manage. So we have seen many scheduling approaches that is already In the webinar, which is hosted at MPUG site. So I have spoken about a number of scheduling approaches, such as you have critical parts method or critical chain method. You have rolling web planning, you have on-demand scheduling or lean scheduling. So we have seen a number of scheduling approaches, in this case, on this webinar, we will be discussing with respect to a very specific scheduling approach, that is the Critical Path Method or the Precedence Diagram Method.

Satya Dash: So I have spoken in the earlier webinar, that is with respect to leaps, lags, and dependencies with Microsoft Project where I have spoken about the scheduling approaches, in that I had informed the scheduling approach with the schedule data and the scheduling tools such as Microsoft Project will give you the schedule model. And that is what a planner or a scheduler or a management professional is actually looking at. So in this case as well, for two-pass technique, we are actually building a schedule model with the help of two-pass technique, which is applied in the Critical Path Method also known as the Precedence Diagramming Method or the PDM.

Satya Dash: Again, like the previous one, I will be here, particularly speaking with respect to deterministic scheduling, that is not probabilistic scheduling. But probabilistic scheduling or non-deterministic scheduling, the approach will be different. You can go for a Monte Carlo simulation, or you can go for a Latin hypercube simulation. But here my approach with respect to two-pass technique and the CPM, we’ll be talking about the deterministic scheduling part. And the approach, as I said, is the CPM, the Critical Path Method, the schedule data we’ll be entering into the scheduling tool that is Microsoft Project, and we’ll be getting a scheduled model, which in effect is your project schedule plan.

Satya Dash: Then the scheduling network, which is created as you sequence the various activities in the schedule, you create a precedence diagramming method in which you’ll apply the two-pass technique. With this technique, the critical path and the total float or TF for short, these values are determined. Now critical path, the definition is, it is the longest path in the schedule network diagram, which determines the shortest possible duration. With this introduction, I’m going to introduce you to certain legends that I’m going to use throughout this webinar. Again, I’m going to cut down all the jargon’s, all the high frequency or high sounding words, because that makes things very complicated.

Satya Dash: And I keep on telling that if things are complicated, you are not going to remember. If you can’t remember, you can’t apply. If you can’t apply, your learning is effectively meaningless and useless. So again, I’m going to simplify and I’m going to speak in very simple terms. So forget about the jargon’s or the dogma or various dogmatic books that you will be following, I’ll be completely simplifying it. So here what we have in the legend, this is the activity in black box. On the top left corner, you have early start, which is ES. On the bottom left corner, you have late start, which is LS. On the top right corner, you have EF, that is early finish. And on the bottom right corner, we have late finish or LF.

Satya Dash: Early start is simply telling you earliest an activity that can start. Late start it is telling you, latest an activity can start. On the other hand, early finish and late finish, they are telling you the earliest activity can finish and latest an activity can finish. And from here to here, as shown in this activity, this will be your duration, whereas, when I’m going to calculate the total float. So total float will be calculated with the help of late start and early start, or we can calculate the total float with the help of late finish and early finish.

Satya Dash: Now, when I move from left to right, for our calculation of early start and early finish, that is called forward pass because I’m moving from left to right, the name is forward pass. On the other hand, when I’m moving from right to left, as the red colored arrow mark is showing, that time I’ll be taking late finish and then I’ll be calculating the late start. And because I’m moving from right to left, it will be called as backward pass. Now because we are using these two passes together, that is forward pass and backward pass, that is why the name of that technique is two-pass technique. And it is the most used technique to determine the critical path as well as the total float.

Satya Dash: So first the forward pass. Now forward pass, as I said, in this case, first we’ll find out the early start. Then what I’m going to do to early start, I’m going to add the duration. This is the duration highlighted in blue color coding. As I add the duration to early start then subtract one, then I’ll get early finish. You may not add or remove one, if it has started with zero or one, but we’ll follow the Microsoft Project approach so that the theory as well as the practical is synchronized. So the formula for early finish will be early start plus the duration minus one. Or in other words, you can say EF is equal to ES plus duration minus one. And from here, of course, you can determine the duration as well.

Satya Dash: Duration will be, you have to just put this into this side and this one also, in this side. So duration will be equal to early finish minus early start plus one. Now, while doing forward pass, because we are moving forward, for all activities succeeding the start milestone on the start will be one. So we will have a schedule network diagram, as I said, we are having a scheduling approach of PDM or the CPM. That is Precedence Diagramming Method or the Critical Path Method. So all activities which are connected to the milestone so that will be a network diagram like this, let us say we have just two activities in this network diagram, this is start milestone, and this is finished milestone.

Satya Dash: So all activities succeeding the start milestone, for those activities early start will be one. We’ll be starting with one. Now EF, for the activity will be calculated by adding the activity duration to early start. But here’s the important point, look for merging or decision points that will have two or more tasks as predecessor of the current task. For example, I can have this task and this task is connected to, say, another task and two more tasks like this two links are there. So at that point in time, look for a merging or decision points. Whenever there is a merging or decision point, the early start for a task will be based on the higher or the highest of the predecessor’s early finish values. If there are multiple predecessors, because early start of the successor cannot be lower when compared with the predecessor’s early finish, it is logically impossible.

Satya Dash: Now formulas will be different when you start with zero, like when I’m saying zero, I said early start will be starting with one. So it is connected to the stock milestone so this will be one. Similarly, for this activity early start will be one. It is possible that some other approaches they use starting with zero, but I’m going to use the Microsoft Project software way because Microsoft Project takes the only start of the activity connected to the start milestone as one. Next is backward pass.

Satya Dash: Now, in backward pass what we are doing, we are first going to calculate the late finish. From the late finish we are going to subtract the duration, so this is again, the duration for the activity. As I subtract the duration after that I’m going to add one, and that will give me the late start value. In other words, late start is equal to, late finish minus the duration plus one. From here, of course, again, you can calculate the duration value. So duration will be, you have to move the duration this side, and then the formula will be, duration will be, the late finish or LF minus LS plus one. Because there can be variety of situations, so you have to know what is the duration? What is the late start? What is the early start? You have to quickly find out, in a matter of minutes. So you should be very familiar with this formulas.

Satya Dash: Now, part of the understanding with respect to backward pass, going backward the late finish of all activities connected to the finish milestone will be highest early finish among all activities. The late start is calculated by subtracting the activity duration from late finish. Like the previous one for forward pass, in backward pass, also, whenever you have a merging point or a decision point, take a step back and look if you have multiple successors, two or more tasks successor of the current task for which you are doing the early start, the late start or early finish, late finish calculations. Whenever there is a merging point or decision point for your backward pass, the late finish of the current tasks will be based on lower or lowest of the successor late start.

Satya Dash: Because the late finish of the current task, which you are considering for your backward pass cannot be higher when compared to the successes late start. Like forward pass before, the formula here, we are going to use starting with one in the formula, for zero if there is another approach, people also use that approach. That calculation would be different, but again, we are going to follow Microsoft Project way because that way theory and practical is going to be synchronized and easily understandable for you. Now, this are various high sounding words, I understand it is not very easy for you to grasp if you are hearing for the first time. This kind of like, multiple successor, multiple predecessor, higher of the two or the lower of the two.

Satya Dash: So what I’m going to do, I will take an example and I’m going to change the color coding. Let’s say blue, and I am saying we have a stock milestone, we have a finish milestone. And we have four activities I’m going to take, let us say A, B, C, and D. All right, and does that connected. So there is a finish to start dependency, or these are the FS dependencies in Microsoft Project lingo among all the task in this schedule network item, and these are the dependencies we have. So what we learned, the theoretical jargon part, you will be getting it in a very simplified manner as we are discussing with respect to this simple example. This is just four activities, you can take this example to 40 activities, 400 activities, 4,000 activities.

Satya Dash: I have seen 15,000 activities in a project plan, MS Project plan. The same principle, the same rule will be applied. So just to tell you the legends, so top left corner, early start. Bottom left corner, late start. Top right corner, early finish. The bottom right corner, late finish. Now I’m going to do a forward pass. For forward pass we are going to move from left to right, and we’ll start with one. Why one, because A is connected to the start milestone. Now A, the duration also I’m going to put, let us put the duration as well. So duration, let us say A is three days. B is five days and C, let us say four days, and this is two days.

Satya Dash: So early start of A is one, it is because it is connected to that start milestone. I’m going to add the duration, so early start plus the duration will give you the early finish. Then you have to subtract one, so one plus three minus one will give you three. Similarly, for C it is one, four is the duration, one plus four minus one will give you the early finish, that is four. Now, how about B? For B, we have a merging point or a decision point because B has two predecessors, A as well as C. Now, which one I’m going to take? I have to take the higher of the two. Higher of the predecessors early finish values, that is what the theory was telling.

Satya Dash: So between three and four, the higher up that two is four. Now, after I take the higher of the two, the predecessors early finish value, I’m going to add one. So I’ll say four plus one, it becomes five, that is the early start of B. Now, five plus five, the duration, minus one will give you the early finish, that is nine. Now for D, D has no merging point or decision point, it is a pretty straightforward calculation. So this is four, or C is finishing on fourth day, so D we’ll start on fifth today. Just add one, similarly, five plus two, we have to add the duration, early start plus duration minus one will give you early finish. So five plus two minus one will give you six.

Satya Dash: So we are done with that forward pass, for all activities now, because we found out the early start, as well as the early finish. Now we are going to do it backward pass. So I’m going to change the color coding. Let us say, I’m going to take this color, purple one. Now, for backward pass, what we are going to do, we have to find out first, the late finish. From late finish, I’m going to subtract the duration, then I’m going to add one. Now, what is the latest that we can finish? Of course, we will finish latest on ninth day. So the late finish of B is nine. Now, nine minus five plus one, will give you five. Now what is the latest that D can finish?

Satya Dash: Many people make a mistake here, they think it will finish on sixth day, sixth day is the earliest that they can finish. The latest that they can finish is ninth day without delaying the finish date. So the late finish of D is nine, and nine minus two plus one that will give you eight. Now we are coming to C, now here we have a merging point. How it is a merging point? We are doing a backward pass. So here we have a merging point again. Now we have to consider five and eight and take the lower of that two, so while doing a backward pass, we’ll take the lawyer of the late start value of the successor. So lower of that two is five, and then we are going to subtract one. So as I’m going to subtract one, I’ll get four. Four minus four plus one will give you one.

Satya Dash: Now for A, there is no merging point or decision point, so nothing to worry here. So five, so it will be one day behind which will be four. Now four minus three plus one will give you two. We are done with the backward pass. So as you can see forward pass, I moved from left to right, but as per backward pass, I moved from right to left. And we found out the early start, the late start, early finish, and the late finish values for all activities. As simple as that. Now, if you understand this, you can scale it as big as you want, and the same principle will be applied. Only caution is whenever there is a merging point, here for B, there are two predecessors, or it can be 10 predecessors so be careful.

Satya Dash: So in forward pass take the highest of the early finish value of the predecessor then add one, but backward pass, we have a successor. Take the lower of the late start values of the successor or the lowest value of the successes and subtract one and proceed. Next is total float. Now total float is the amount of time that a schedule activity can be delayed or extended from its earliest start date without delaying the project finish date or violating a schedule constraint. Now, schedule constraint can be a flexible constraint or the non-flexible constraint, or it can be a semi-flexible constraint. But most of the time as a scheduler or planner, if you have a hard constraint or a non-flexible constraint, that time you have trouble.

Satya Dash: Simply speaking, total float is telling by how much time you can delay in activity in a network diagram without delaying the project finish date or the end date of the project. And that is very important for you as a scheduler or a planner because your performance or your performance appraisal, one of the parameters will be how … Were you able to complete the project on time? That will be one of your KPIs, the key performance indicators. Now, what is the significance of total float? Total float or the critical path activities will have total float value zero. The formula for total float is, total float is the difference between late start minus early start, or it can be late finish minus early finish.

Satya Dash: Now, what does it mean? We’re going to re-use the example, the same example, which I just explained. Now I have already calculated the early start, the late start, early finish, late finish for all these activities. We have, again, I’m putting the legend, ES, LS, EF, and LF. So we have to find out this difference, two minus one will give you one, so that is your total float value for activity A, equal to one. Similarly, this side also same, four minus three, that is late finish minus early finish, or it can be late start minus early start. So total float for A is equal to one. It is not zero, that means, it is not a critical activity or critical path activity. On the other hand for C, we have one minus one or four minus four. This is giving us a value of zero, so here, total float is equal to zero.

Satya Dash: For B, five minus five, this side or this side, nine minus nine. Here again, the total float is equal to zero. This is a critical path activity. And four D, nine minus six or eight minus five, as I said, total float can be this side or total float can be this side. Either way you can take, and this total float is coming is three. So whenever, as I said, the total float value is zero, that is our critical path. So that means this is our critical path, if I draw a line. And this is the path which is the path, if you delay any activity on this path it is going to push the end date, and you are in trouble with respect to time. For example, if I delay C by just one day, it will be five days. It will be finishing on fifth today, and this will be six, then this will be 10.

Satya Dash: So instead of finishing on ninth day, you are going to finish on 10th day. Why one day? Even one minute you delay, just futuristically speaking, again, your end time or end date is getting delayed. So the total float value for the critical path activities will be zero. Whereas, for the non-critical activities, such as A and D the total float value will be non-zero. Now, the questions that will be coming to your mind, how about the early start, late start, or early finish, or late finish values for the milestones. How about them?

Satya Dash: Now, for milestone, what will happen? Theoretically speaking, milestone is an event it is not an activity. So the duration is zero for milestone, in other words, this gap, it is the gap between early finish and early start or late finish and late start, which is our duration, this is zero. Or in other words, early start will be equal to early finish, late start will be equal to late finish. All will be equal here, early start, early finish, late start, late finish. All will be equal because milestone is a significant point in your activity, which is of non-zero duration, theoretically. Of course, Microsoft Project gives you a flexibility to have milestone greater than zero, but by default, milestone value will be zero.

Satya Dash: Similarly, for start as well, early start, early finish, late start, late finish value here all will be equal so this will be zero, and this will be nine or 10. We’ll see shortly with more examples on that with the help of the tool. Next is, what happens when a constraint is applied? Now, constraints are part and parcel of management, because as a project manager, you are audit program manager. You will be handling your project with multiple constraints, and if there are constraints that are applied, what will impact on the total float values? Another question will be coming to your mind, will the schedule be feasible if a constraint is applied? Let us see the first activity part here.

Satya Dash: So I’m going to change the color coding again. Let us say, I’m going to take green. Okay, now let us say, I’m having the finish, your boss or your supervisor told, “No, no, no, we cannot finish on the ninth today, you have to finish it on seven today.” So fine, so this is seven. In other words, the latest that activity B can finish is seven. Now if this is seven, what will be this one? We’ll apply the same formula, seven minus five, the duration, then we’ll add one so it will be three. So this is again, seven for B. Latest we are saying your manager said, “No, no, no,” maybe you’re going to the vice president or your CTO, and he is saying, “No, we have to do it,” instead of days let us say it is weeks. Instead of ninth week, it has to be done in seventh week, we cannot delay. So seventh week fine, so seven minus two plus one in this case will be six.

Satya Dash: Now what happened here? Now, what is the total float value here for B? Now this is seven, that is the late finish is seven, early finish is nine. So seven minus nine, what will be the total float value? Here will be minus two here, or three minus five, either way it is minus two. The total float value is minus two for B. How about D, total float value is seven minus six or six minus five so this is positive one. How about A? Let us calculate again, so this is three, this is six, now going backward I’ll take the lower of the two, which is three and subtract one. So three minus one will give you two. Now two minus four plus one that will give you, two minus four is minus two plus one, will give you minus one.

Satya Dash: So what is the gap here? Two minus five, so total float here is minus three is the total float value. Similarly, two minus four, sorry, not five, two minus four it will be minus two. Similarly, minus one minus one, so total float value this side is also minus two, isn’t it? So this is minus two. This is minus two. This is positive one. How about this one? [inaudible 00:29:09] I’ll subtract one so this will be three. Now three minus three plus one will give you one. Now we have a zero lag. Now, what is the problem in such a case if you have a hard constraint applied to your faucet? In that case, you are getting the total float value as a negative. Any time in your schedule, if you will find the total float value is negative be very clear.

Satya Dash: The schedule is not feasible. The schedule is really pulling you apart. So find out ways how to get that total float value as a non-zero one, because it becomes an impossible schedule. So what you are going to do if you have a total float value of negative? In that case, you have a number of options. If you are really a management practitioner you can do a crushing, or you can add a number of resources to add the, that is, reduce the duration for your task or activity. Or it can do some fast tracking, or you can reduce the scope and find out a way or split the task, with a tool also you can do all those things, but ensure the total float value is a non negative number. That is zero or it can be greater than zero, that way your schedule is easily feasible and achievable.

Satya Dash: With is theory, let us now move to Microsoft Project, the practical aspect of it, and how Microsoft Project handles two-pass technique. So first there are some fields, in-built fields available in Microsoft Project. The fields for forward pass are, early start and late start, it is perfectly matching with respect to the theory side. For the backward pass, the fields that you are going to use in Microsoft project will be early finish and late finish, which is again, perfectly matching with the theory. Then we have to find the critical path, for critical path, we can see it in the Gantt side and the Gantt chart side of the Microsoft Project or you can see in the table off site as well.

Satya Dash: For the table off site, you have another field called critical, which is basically a Boolean value or a flag, which will tell you yes or no. If it is a critical activity, then the value will be yes, if it is an uncritical activity, then the value will be no. Now total float has a slight different name as Microsoft Project calls it, Total Slack. Instead of float, they have a name called Slack, and total float is called as Total Slack. Or simply speaking, float is replaced with a name called Slack in Microsoft Project software.

Satya Dash: With this field the background, let us see how Microsoft Project actually calculates that total float and early start, late start, early finish, late finish, and does the forward pass and backward pass calculation. Now here, to work with Microsoft Project software you have to switch to a table called schedule table. A default Microsoft Project will be entry table, and your view will begin chat with timeline. It will show when you switch to the schedule table, you will have all these values, TF, LS and LF. You have to add for other ones. Alternatively, you can add the following columns in current view of your table and then save it as a custom table. For example, you are in entry table, in entry table you can add this early start, early finish, for forward pass, late start and late finish for backward pass. And Total Slack you can add because there’s an in-built field available and you can save it as a custom table.

Satya Dash: So let us do it now and see how Microsoft Project does it. So here I have an example in PB file, and I’m going to open this file. And this is empty right now, and we are going to use or reuse the same example that we saw some time before in the theory aspect so that you can easily correlate. So I opened it and here the default view is Gantt chart, I have disabled a timeline view. Then the tasks are actually auto schedule, I have kept it for simplicity purpose. So we’ll have start the milestone then A, B, C, D we had four tasks and then finish the milestone. A, okay, so the table is actually changed so I’ll [inaudible 00:34:00]. This will be our default table as you open, duration, start, finish, predecessor, resource, this will be shown in case you are trying it on your own right now, you can see it on your own.

Satya Dash: So A was three days. B was five days. C was four days, if I remember correctly, then it is two days. Then finish is a milestone zero, and this is zero. Now we are going to have the linking among the tasks and milestone. A’s predecessor is start, so it is one. B’s predecessor is A as well as C, we had two predecessors. So three here, two and four will be the predecessors. For C, we had start again, for D we had B as the predecessor as well as C as the predecessor. C is four. So C is the predecessor. So now this is coming, so this is finish to start, AB connected, then finish. Finish, of course, is connected to D as well as B, so D and B. Three and five.

Satya Dash: Okay. So is it correct? I think we had a … So this is connected, C is connected to … Okay, I’m going to, now, this is not clearly visible, it is creating a bit of confusion. So I’m knowingly putting it this way, I’m going to change, I am going to highlight what are tasks on the right-hand side. So what I’m going to do, I’ll go to format tab, and here I’m going to change the bar. Now here in bar text, it has bar shape and bad text. So I’ll go to here and on the top, I’ll put the name of the task and inside, I’ll have the duration of the task and I’ll say, okay. As I do that, so now it is clearly coming A, B, B is connected to finish. D is also connected to finish, but D has a problem. So D is connected to only C so that is the problem we have.

Satya Dash: So I’m going to change it, and it is connected to only C. Now it is perfect, isn’t it? AB, finish to start, then B is connected to finish. Then C is connected to B, C is also connected to D, and D is connected to finish. Now, because I added the name of the task and the duration of the task, it becomes much more easier for me to look, but still it is not that much visible. So what I’m going to do is I’ll increase the length of the bar, let us increase the length of that bar. So again, I selected on top left corner, as I select the top left corner so it is electing the entire table. Now I will go to format layout, on that format subgroup under that. So it is the format in the ribbon, format tab, under that we have format group, under that I used layout command.

Satya Dash: And here instead of bar height as 14, I’m going to make it the highest 24. Then date format is fine for us, 1/28. You can change the date format here as well, the link you have various options you can do that as well. Rest are fine and I can say, okay. As I did that, of course, the bar size increased and it is much more visible. So with this, now we’ll be thinking, I’m going to save this plan and draw less, or you can save it on the Quick Access toolbar. I’m going to switch to the table of schedule table. So tables by default is entry, I’m going to choose to schedule. Now, as I switch to the schedule table, can you see, we have the task names, start, finish, then early finish and late finish. Then you have free Slack and total slack.

Satya Dash: I’m not concerned about free slack for this webinar, so I’m going to hide it. My job currently is to look at the total slack, that is the total float value and of course, we have to add a couple of more columns. So I’m going to insert another column, we have early finish and late finish, so I’m going to add early start, another column early finish. So to add a column I just right-clicked and insert a column. So you select any column on the table and right-click and insert a column, and as you insert a column, so Microsoft Project is smart enough to tell you what is the column that you want to add. As you type it will be showing those names early, then all the values are populated.

Satya Dash: So I have early start, early finish. Okay, so I’ll hide this column [inaudible 00:38:43] early start, early finish then … So here I’ll hide this column, I’ll say late start and late finish. It is late start and add another one late start. So have early start that is ES, late start, that is LS. Early finish that is EF, late finish that is LF, and the total slack it is auto calculating for you, and it is giving you one, zero, zero, three and zero. If you remember, it perfectly matches our theoretical part. Let us go back to the slide so you agree. So here the total float is one, the red one. After I put the constraint, then there is the green color coding. Without the constraint, the red one. So total float for A is one, for C it is zero, for B it is zero, for D it is three.

Satya Dash: In the practical side, for A it is one, B it is zero, C it is zero, D it is three days, perfectly matching. How about early start, late start, early finish, late finish? Let us take an example, let us take A. So A is saying, early start of A is Monday 11/2, and late start is 11/3, Tuesday. And early finish is 11/4, late finish is 11/5. Let us go back. So it is Monday, early start and late is Tuesday, that is early finish for the late start. Early start and late start, Monday and Tuesday, so this is perfectly matching, one and two. And this one for A, the late start and, sorry, the early finish and the late finish. So early finish is three, late finish is four. So again, it is perfectly matching.

Satya Dash: So early finish and late finish, they’re also perfectly matching for activity A. Similarly, for activity B, activity C, D, this all will be perfectly matching for you. The good part is you don’t have to calculate, just four activities, but you’ll be definitely not having four activities in your project you are likely to have at least 400 activities. I have seen other tools sometime before thousands of activities. Now, how we are going to address thousands of activity and do a calculation? Long back, I think sometime in 2007 or 2008, while I was getting introduced to project management, my first job into a role of a project manager, long back around 213 years before.

Satya Dash: So I met a person who is a very senior guy, I think he was a general manager in an aircraft manufacturing company. And he was saying that they had this network diagram, the precedence network diagram vested across the walls. There are some thin walls and they have drawn the network diagram across thin walls in the office complex building. Imagine the problem they have, you have to just go and draw the early start, late start, early finish, all the calculations that you have to do. On the other hand, if you have a software tool, it is compact. It is available on your face and it is auto calculating everything for you. Isn’t that great? And this is what the utility of the software tool that we are using here, and that is giving you all the values.

Satya Dash: Now, as I said some time before, you can save it as a custom table, so I’ll go to tables and I will say, Save As, table will be under View tab, data group tables and I will say, save field as a new table. And I will say, let us say two-pass table, and I’ll say okay. Now, the advantage is, in case you switch to entry then you forgot which table, like you forgot the columns, then you don’t want to add, so you can switch again, custom table you have two-pass table. So back to two-pass table, you can come here. Now you’ll be thinking, what is the critical path? As we know, critical path, the total float will be a total slack as Microsoft Project calls it, will be zero. And it has also in-built field, the in-built field is critical, as I said.

Satya Dash: So I’ll hide, again, right-click insert column, and I’ll say critical. And so it is saying, A is non-critical, B and C there’s that two critical activities, late start non-critical activities. It is perfectly telling you. Now, in the graphical side, we see the critical path simply go to the format tab, and Microsoft Project has a very handy check box here the critical task, just enable it. As you enable it, it directly told you these two are critical tasks which are highlighted in red color coding. If it is highlighted in red, that means these are critical tasks and the total float value for these two critical tasks in the network diagram, which is available here is giving you a value of zero for both.

Satya Dash: Now, can I show the slack, the total slack in the graphical side? Is it possible? Absolutely. You can show the slack in the graphical side, but what people make a mistake, they just enable the slack here and they say, “Oh, this is the slack.” No, I have seen almost everyone of them, I have seen a number of articles, number of books, almost everyone is saying, this is the total slack. This is not the total slack, this is the free slack. So be very clear, this is not the total slack this is the free slack. We want to find out what is the total slack, why I’m concerned about total slack? Because free slack, the resources among themselves they’ll sort it out. What is the gap between the two? The predecessor and successor.

Satya Dash: Free slack is basically telling you how much time you can delay an activity without delaying the successor activity. I’m not really worried about that because my job is a high level, if you are working as a project manager. If you’re working as a program manager, again, it is at a much higher level. Or if you are working as a portfolio manager, it is again, much, much higher level. So even at the project manager level, if you have 400 or 4,000 activities, you really don’t have time to look at the free slack, that is how much time you can delay an activity so the successor activity is not delayed. Your main job is to protect the end date, the finish date, and that is why the total slack or the total float value is of crucial importance.

Satya Dash: So here, what I’m going to do, I’m going to show you, this is not the total stack, this is actually the free slack. How I’m coming to know, again, I’ll select this table entirely top left corner, I select it. And I’m going to view project tab, no, it will be under format tab. Okay, yes, format tab, bar styles, and you have to go bar styles. And as I go to bar styles, I’ll repeat. So you go to format tab, bar styles, and format, or you can type it. I should have typed it, there is a feature called, Tell me What you Want to Know. This is a feature so you can type format, so it will automatically tell you. Anyway, we have come here, so I’ll go to format tab, bar styles, and bar styles. And as I go there, it pops up another dialog bars, I scroll down and you’ll see it is saying slack, the name is slack, which is the check box we enabled. This check box we enabled.

Satya Dash: The appearance is this color coding, which looks to be purple. So four tasks, which are active tasks, some task finish and two free slack. And you see it is for free slack, it is not for your total slack. So what I’m going to do, I’ll add another column, another rule here. I will save that as a total slack and for the bar, I’m going to take, the shape will be this one, let us say slightly less. Okay, this one, and this would be solid. The color coding, let us say, we’ll take orange. Is there anything orange available before? Yes, we have. So I’m going to change the color coding to another one. So let us say the color coding will be, say green. Okay. Now it will be again, I’ll say it is active tasks start and here I’ll say, not tasks start. We are going from task finish so we’ll have task finish.

Satya Dash: Then I’ll even have a dropdown or you can directly type and I’ll take total slack. As I did that, I’ll say okay. So this is your total slack. So this is your free slack. Now, the value is not shown to you so in this case, so what I’m going to do, again, I can select go to format. So here itself, I can say right-click and say, what is the number of days or duration? For example, let me do it so that you don’t get confused. Again, I’ll go to the bar and on the right, I’m going to say total slack. The same thing, what we did before. So I’ll say, okay. And as I say total slack for A, it is one day, but this is zero, these are critical tasks I’m going to display, zero, zero. And for D, the total slack is three days.

Satya Dash: So do not use this slack value as a total slack. Almost everyone I have seen, they’re saying it is total slack. It is not. It is free slack. For total slack, I just showed you how you are going to show that total slack in Microsoft Project software. Now, how about constraints? If you apply a constraint, as we have seen, a hard constraint, then the float value will be negative. So let us see that as well. So let us say, we’ll use the same thing, we are going to complete on that seven today. There is input, no, we cannot compete on the ninth day, we are going to compete on the seventh today. So I’ll double click on that finish task, go to advanced, and in that we have constraint type. So we have, these are flexible constraints. As late as possible, as soon as possible, then you have FNET, FNLT, SNET, SNLT.

Satya Dash: I’m going to have a hard constraint, MFO that is must finish on, or MSO, that is, must start on. These are non-flexible or hard constraints. So the idea is, two days before, so it is finishing on 12th, which is finishing. I’m going to do this before, that is seventh day, working day. So 11/10/2020, and then say, okay. Now, as I did that, there is a message, “That will be a violation of schedule conflict, we you want to continue?” I’ll say, okay. Another message, “This will result in another conflict, a conflict of schedule. Will you definitely want it to continue because we want to see?” So I’ll say, okay. Now, did you see when I did that, the total float values just changed to minus two days for finish, for D it is one, but C it is minus two, for B it is minus two, for A all negative.

Satya Dash: Now the total slack is coming is negative. It again, matches with our theory because when I said it is seven, this becomes seven, right? And this is nine. Now, seven minus nine is minus two, matching. Now here, this is seven, seven minus six, it is plus one, still matching. For D it is … For C it is minus two whereas for D it is one. So theory is matching perfectly with the practical. As I said, if the total float is negative, if you see a number of total float value or slack value is negative, your schedule is really in trouble. So as much as possible, try to solve it before you start proceeding on it.

Satya Dash: Now, coming back. These are the final key points I have as I’m coming to the closure of this webinar. So the total float informs on the schedule flexibility, because total float is telling by how much time you can delay an activity without delaying the project end date. So if you have 10 days of total float, that means you can delay an activity for 10 days without impacting the end date. So you have a high schedule flexibility. Next is, a puristic approach of CPM, that is Critical Path Method tells the total float value should zero for projects critical path. However, the total float value also can be positive for critical path, which you just saw. Without applying the constraint, if you remember, some of the activities has total float value of zero, some of the activities are one and three days, which are non-zero activities.

Satya Dash: Now, next point is, while working with two-pass techniques, when you have scheduled constraint, it is possible that the negative total float value can arise, so which you just saw. I just applied a hard constraint and we got negative total float values. So as a planner, scheduler or manager, ensure that you do not have negative total float values. Because as I said, if negative total float values the schedule is not feasible. You’ll be surprised, there are so many people who bring me plans, and I see so many negative total float. I say, “How you prepared the plan?” “No, I applied a lot of deadlines, a lot of constraints.” “No, it is not going to work. You cannot really work on the schedule.”

Satya Dash: So this is a common mistake I have seen. So try to solve it if you have negative. So that is called, negative total float analysis in theoretical project management languages. Next key point is telling you, closely track the total float with positive values. Because if one activity is consuming it, then it will not be available for other activities. What it means is, in the diagram that we saw, for A it is one day, for B it was zero, for C it was zero, activity C. For D it was three days. Now, if the total float value in that same line, you have some positive value and another activity has some total float. That total float is consumed for not only for the activity, every activity on that line. So that is what it is telling because if one activity is consuming it, it will not be available for other activities.

Satya Dash: The final key point is telling you, a rapid consumption of total float values can indicate a possible slippage of schedule and hence, a schedule risk. So if your total float values are getting consumed or getting exhausted very rapidly, that means you are heading towards the schedule risk. So be careful in that aspect as well. So we just saw, to recap, I introduced where it is used, the two-pass technique in Critical Path Method approach. Then I spoke about the legends, I simplified it completely. You will find a lot of diagrams telling that, they will say, you start here. They will be having a box, many boxes. They’ll be drawing boxes. Then here, they’ll say early start. Here you put total duration. Here you put total float. So again, there is no need to follow this kind of dogmatic approach, if you understand, this is plain mathematics, you can draw it on your own.

Satya Dash: Next, I explained what is for what path. Next, after that I told you, what is backward pass then how these two are having together, calculations, I showed you an example. Next, I went to that total float calculation. After that, we went to Microsoft Project. I created a fresh plan for you using that theoretical example. I have show you how you are going to find out the early start, the late start, the early finish and late finish values. The total slack value as Microsoft calls it. Then how to see the total slack, many people take the free slack and tell it is the total slack. It is not. And I also increased the bar size, the duration, the name of the task, the slack value on the right side, I show how you can format and how to have the total slack. Also, another type of formatting I showed it to you.

Satya Dash: And in the end also, I showed you how to avoid negative total float, in what situation, there are many situations you can have negative total float. I showed one particular situation, which is, if you are having hard constraint of must finish on, MFR we said. And that is where I said we have negative total float value. With this, I’m coming to an end and I have some time. So Kyle, over to you, and I were taking the questions. These are the references, I have taken PMP Live Lessons. MS Project Live Lessons, these are prepared by me. The definition of critical path and total float value, I have taken it from the PMBOK Guide, that is Project Management Body of Knowledge Guide.

Kyle: Thanks, Satya. And just a reminder, if you could return back to the previous screen, we do have a screenshot button at the top of the viewer window. So if anyone is interested in checking these links out, hit that screenshot icon, and that’ll save a screenshot to your computer there. If anybody has any questions, we do have a couple minutes here, we can take those live. So feel free to chat those over. One question we had was from Renee, and she was curious if it’s possible to get copies of the charts that you showed in the PowerPoint presentation.

Satya Dash: Sure. You can send me Renee your, or you can drop me a mail. I’ll share my email ID towards the end, and I will share the slides with you. I have no problem with that.

Kyle: Great, thanks.

Satya Dash: Yeah, drop me a mail on my email ID, I’ll share towards the end and you will definitely get the slide deck.

Kyle: Okay, perfect. And then, Mike just asked about the recording. This session is being recorded and we will share a link in just a couple hours, you’ll be able to view that on mpug.com. All of the sessions are recorded, so you can always access any of these sessions later or anything we’ve done in the past. It’s all available to you on mpug.com. Let’s see here, we’ve one more coming in. So Kyle is asking, first says thanks for the outstanding presentation, Satya. Does this technique work for the projects using Agile Development Methods?

Satya Dash: Okay, Kyle, it’s a good question, and I get this question pretty frequently. So Kyle, thank you for appreciating the presentation. I hope it was helpful for you. Now, coming to your question on Agile. Now, Agile, If you look at it, Agile is an umbrella term. Agile is not a particular methodology or an approach. So when you say Agile, is it Scrum? Or is it Kanban? Or is it Lean? Or is it DSDM? Did you mean you about having Scrum? Now, Scrum because that is the most widely used one. So if you are using Scrum the iteration duration is fixed in a Scrum, two weeks to four weeks. Within four weeks you have to deliver even in iterative and incremental version of a product.

Satya Dash: So because the duration is fixed, the iteration duration is fixed. You don’t have a concept of critical path because the duration is anywhere fixed 14 days or 10 days, if you are including only the work days. So if you have 10 days of fixed duration, you don’t have a concept of critical path. So because you don’t have a concept of critical part, you don’t have a concept of total float or forward pass, backward pass, it doesn’t apply. Now, let us take another one, Kanban, which is primarily from Lean. Now Lean, if you look at it in Kanban approach, the focus is on the flow. The focus is, this is an on demand scheduling, the focus … Kanban doesn’t restrict you to an iteration. So flow in a sense, first to come first to go.

Satya Dash: So how quickly you are delivering, you can have delivery on the third week or on the sixth week. You can have your own customized delivery time. The focus is not critical path best approach. As I said, from the very beginning, I said, you have to determine your schedule approach. If your schedule approach is Critical Path Method, then you can apply the two-pass technique to determine this values. If your scheduling approach is, let us say Kanban or Lean or say on-demand scheduling, in that case, you don’t get value out of it. In other words, simplifying, in a deterministic schedule, that is non-probabilistic schedule, you can apply the Critical Path Method and have total float and all this ES, LS, EF and LF values calculation. Whereas, in an on demand scheduling, Scrum is semi on-demand, Kanban is almost fully on-demand.

Satya Dash: In Scrum, as I said, the iteration duration is fixed. So there is no concept of critical part because the duration is anyway known to be 10 days, you have to deliver in 10 days. So why worry at all what is the longest path when the finish date will be delayed? Because it is a hard finish you have to do. If you cannot deliver in the same iteration, you have to move that item or that product backlog item in the next iteration. So it doesn’t apply.

Kyle: Okay, great. Thanks, Satya. And that takes us right up to the end here. Would you be able to share your contact info for anyone interested in reaching out?

Satya Dash: Sure, Kyle. So before I go, I have a couple of slides to go. So what a year it has been, right? In a way it is the longest of years, like every year, it is also the shortest of years. Because the time flies and I am very much aware how hard it has been for all of us, the people who are listening to this webinar. So I take this opportunity to wish you a very happy new year, 2021. I wish you and your family members, a very happy, prosperous, and a meaningful new year in 2021. And with that, thank you for listening and thank you for your time. And here is my email ID, that is, managementyogi@gmail.com. And this is my site, that is, managementyogi.com.

Satya Dash: Some of you have … I get a number of questions after they complete the webinar. You can definitely introduce yourself, the attended webinar, and I have this question. You will definitely get a response from me. I responded to all my questions if you have attended the webinar. And another person had a question with respect to slide deck, you can drop me on this email ID and you will get a response. So thank you again, and thank you, Kyle, for facilitating this discussion.

Kyle: Excellent. Thank you so much, Satya. We really appreciate your time today and covering this material, and demoing it for the MPUG community. We really appreciate it. Those of you that are claiming the PDU credit for today’s session, I’ll get that back on the screen for you. Today’s session is eligible for one technical PDU. The activity ID you can use to claim that with PMI is on screen now. And if you missed any of the session and would like to go back and review anything that Satya shared with us, as I mentioned before, the recording will be posted at mpug.com a bit later today, and you’ll receive an email in just a couple hours and the link to that. MPUG members have access to our full PDU eligible library of on-demand webinar recordings.

Kyle: And we do have some great sessions coming up on the calendar. November 18th, Dharmesh Patel will join us for tips, tricks, and clicks on effective project management using Microsoft Teams. That’s a 45 minute session, and on December 2nd, highly requested presenter and topic as well. Ira Brown will join us for working with Microsoft Project master schedules and sub-projects. Both of those sessions are open for registration, and I just chatted over a link along with some others. Satya will actually be joining us again in January. So keep an eye out for that session, it’ll be on the calendar shortly. And that wraps it up for today. Once again, thank you, Satya. And thanks everyone that joined us live or is watching on-demand. We really appreciate it, and we’ll see you back soon for our next live session. Thank you.


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Written by Satya Narayan Dash

Satya Narayan Dash is a management professional, coach, and author of multiple books. Under his guidance, over 2,000 professionals have successfully cracked PMP, ACP, RMP, and CAPM examinations – in fact, there are over 100 documented success stories written by these professionals. His course, PMP Live Lessons – Guaranteed Pass, has made many successful PMPs, and he’s recently launched RMP Live Lessons – Guaranteed Pass and ACP Live Lessons – Guaranteed Pass. His web presence is at https://managementyogi.com, and he can be contacted via email at managementyogi@gmail.com.


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