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I ‘solved’ my problem but I’m really having a hard time wrapping my head around the explanation. I have some fundamental misconceptions about Task Type which has caused me a lot of grief.

I have 2 tasks assigned to different resources both nominally of 2 wks duration with task type of Fixed Units- One was 80 hrs and the other 16 hrs. Both have identical predecessors. Though they are nominally 2 weeks in duration the 16hr task appears a tiny bit longer on the gantt chart and has zero days of slack. It’s doppleganger has 1 day of slack.

Five predecessors upstream in the critical path I extended the duration of a fixed duration, critical, task by a single day and everything between that extended task and the 16 hr task gained a non-zero slack and, thereby, was dropped from the critical path. Everything in that chain had an ASAP constraint type.

I’m struggling to understand why the intervening 4 tasks gained non-zero Total Slack values. Converting both tasks to fixed duration restored the Total Slack values for those 4 tasks to zero.

I would love it if someone would do a deep-dive webinar on critical path puzzles like this.