Every project starts with a rough estimate, and these are usually referred to as preliminary. As the project progresses, the actual task performance may be different from the initial estimate. This difference is called variance.
On page 16 of PMI’s Practice Standard for Project Estimating the authors write, “Even though estimates are developed initially at the onset of a project, it is important to think of estimation as continuous activity throughout the project life cycle.” The important words here are “estimation as continuous activity.” In other words, estimates of current and future tasks should be validated and revised periodically.
Is this feasible? Yes, provided the project manager applies his or her skills of observation and decision making.
As the project progresses, the project manager should observe the following areas to measure efficiency and do research to identify the root cause: scope and technology, the team, and the process.
With respect to scope and technology, the observations should be on its complexity, stability, support, and interoperability. Within the team, observe participants’ attitude, capability, motivation, and performance levels. In terms of process, the observations should be on identifying inconsistent, ineffective, and inefficient steps.
The next logical step is to take actions based on the observations. First, revise the (time, cost, and resource) estimates. Second, publish the forecast.
In Microsoft Project, use the Tracking table of the Detail Gantt view (in the View ribbon, Data group) to record the actual work progress. Also revise the forecast on the remaining amount of time, cost, and resources based on the actual performance.
After revision, use the Variance table to measure the schedule slippage.
Forecast the scheduled start and finish using the Entry table of the Detail Gantt view.