Free Slack Question

[nnigeltaylor]

Hello All,

I have a forthcoming project but I’m having problems getting to grips with resource scheduling as I’m a complete novice in the field of project management and only trying to get the hang of it.

Out of the 23 tasks outlined for the project (find attached) 3 of the non-critical tasks possess 39, 52 and 23 free slack.

Question: When I tried to increase the duration on the tasks that possesses free slack it did not seem to have profound adjustments on the critical path. I am wondering what I have done wrong?

 

[PDQBach]

Thank you for reposting over here.

I'm not really sure what you were expecting to see. But, having said that, I'm not even sure that your objective is a worthwhile investment of your time.

The whole idea of Slack is determine which tasks/deliverables are on the Critical Path and to then focus on those tasks since their delay will impact the overall project schedule completion.

In addition, by accurately tracking task Actual Start and Actual Finish, as well as adjusting the estimated Durations of active tasks (to reflect revised Finish dates), you'll see that the Critical path is dynamic and tasks that previously were on it may be dropped and tasks that previously weren't on it are now shown.

When it comes to resource leveling then, again, you really don't want to focus too much on Slack but, rather, on the actual tasks themselves. If you have an overloaded resource then you need to see if the tasks where the overload occurs are on the critical path. If the tasks aren't on the critical path then you *might* want to consider increasing the duration of one (or more) of those tasks -- but if they're not on the critical path and your resource has given you reasonable estimates and the overallocation is reasonable then you probably don't have to worry about these tasks.

Alternatively, (if the tasks are on the critical path) consider if those tasks shouldn't be done by two different resources (to attempt to maintain the originally scheduled project completion) or, alternatively, have those deliverables done sequentially rather than in parallel so that the original resource (the "correct" resource since he/she is best suited to provide the deliverable) is still assigned and the schedule reflects the reality of predecessors/successors. This may very well extend the project duration and may (will!) impact the tasks flagged as being on the Critical path.

Finally, as I harp on about constantly: your schedule is only as good as your estimates. Depending on the industry and project deliverables, your estimates may be no more than +/- 50% accurate. If that's the case then your time is going to be best spent carefully tracking actual progress, revised Work and revised Finish dates. As you update those, then go back to your Critical Path to see which tasks are now on it ... and watch those like a hawk!

 

[nnigeltaylor]

Splendid, sincere thanks for sharing your expertise, I have taken this on board.

One last question, what is the implication of setting tasks without predecessors? I noticed that the tasks with the extremely high free slack (15, 16 and 20) are those without predecessors. My colleagues in the engineering team have probably not determined what impact their schedule would have on the other functional areas and left out the 3 tasks without predecessors. Are the missing predecessors the reason for the very high slack numbers of 23, 39 and 52 in comparison to the rest?

 

[PDQBach]

Setting tasks without predecessors. Ah, yes. I could talk for hours and on this and cover both sides of the argument: (1) it's never a problem, go for it; and (2) gasp! sacre bleu! Never!!!

My answer: it all depends on your schedule management style.

In my personal case:
(1) I try to avoid puting predecessors/successors on Summary tasks but will occasionally put a successor on a summary task to a specific detail task elsewhere in the schedule.

(2) I *generally* use predecessors and successors

(3) I *generally* do not have a nice waterfall cascade in my Gantt charts. Instead, I'll have a group of tasks that are all Start-to-Start links showing that they will take place in parallel. I do that partly because I know the resources will work ahead on one task until a roadblock (or ennui) and then will work ahead on another unti a roadblock (or more ennui) at which point they will either start a third task or resume the first.

The nice thing about this is that I'm not constantly having to reschedule tasks because one task (of a related set of tasks assigned to a specific resource) is late.

The two things I *do* keep on top of are Finish dates and Work remaining. For a given task (or for a group of related tasks) it's not that vital ... but when considered overall with the specific resource availability, I can make certain resources aren't overloaded and, simultaneously, keep track of the project finish date.

Finally, one other related thing: 8/80. (That's in hours.) A deliverable should never have less than 8 hours of Work nor more than 80 hours of Work. Too few hours, and you're micromanaging; too many and it's too easy to hide lack of progress.

Okay, one more "one other related thing": sortof8/sortof80. (That's in hours.) A deliverable should never have less than "sortof8" hours of Duration nor more than "sortof80" hours of Duration. I'm more flexible here because sometimes a deliverable (a printed report, for example) will go through several iterations over a slightly extended period of time because column alignment can be a challenge.

 

[procygnus]

Nigel - there appear to be many common beginner errors in your plan that you may like to rectify in discussion with a mentor. I will list some below as it comes to my head:

1 Calendar: you are using the standard calendar with default work hours
2 Task Duration - you have fractional durations, probably unintended
3 Work - fractional workhours
4 Resource assignment - both 2&3 are caused by "second" assignment
5 Modularization - Plan not modular (by function/deliverable)
6 Use of milestones: Missing
7 Summary Task: Its a default feature in Tools/Options/View tab
8 Task type: All tasks use default settings "Fixed Units" Effort Driven=True.
9 All tasks use default calendar, whether critical or otherwise
10 Level & Baseline: Project not leveled or baselined.
11 Completion criteria: Tasks such as design need definitive completion criteria as they go through an iterative process of drafts, reviews, approvals, notice to tender, eval etc
12. Project Buffer and Contingency?
13. Project management effort?
14. Decision turnaround time?
15. List of Assumptions? (Use Task Notes)

It shouldn't take longer than 8-10h to learn the basics from where you are today.

Best wishes.