Twice as long and half as long
- by PointsToShare
We are in a project and we hit some snags. What’s a snag? An activity that takes longer than expected. Actually it takes longer than the time assigned to it by an over pressed PM who accepts an impossible time table and tries his best to make it possible, but I digress (again!). So we have snags and we also have the opposite. Let’s call these “cinches”. The question is: how does a combination of snags and cinches affect the project timeline? Well, there is no simple answer. It depends on the projects dependencies as we see in the PERT chart. If all the snags are in the critical path and all the cinches are elsewhere then the cinches don’t help at all. In fact any snag in the critical path will delay the project. Conversely, a cinch in the critical path will expedite it. A snag outside the critical path might be serious enough to even change the critical path. Thus without the PERT chart, we cannot really tell. Still there is a principle involved – Time and speed are non-linear! Twice as long adds a full unit, half as long only takes ½ unit away. Let’s just investigate a simple project. It consists of two activities – S and C - each estimated to take a week. Alas, S is a snag and really needs twice the time allotted and – a sigh of relief – C is a cinch and will take half the time allotted, so everything is Hun-key-dory, or is it? Even here the PERT chart is important. We have 2 cases: 1: S depends on C (or vice versa) as in when the two activities are assigned to one employee. Here the estimated time was 1 + 1 and the actual time was 2 + ½ and we are ½ week late or 25% late. 2: S and C are done in parallel. Here the estimated time was 1, but the actual time is 2 – we are a whole week or 100% late. Let’s change the equation a little. S need 1.5 and C needs .5 so in case 1, we have the loss fully compensated by the gain, but in case 2 we are still behind. There are cases where this really makes no difference. This is when the critical path is not affected and we have enough slack in the other paths to counteract the difference between its snags and cinches – Let’s call this difference DSC. So if the slack is greater than DSC the project will not suffer. Conclusion: There is no general rule about snags and cinches. We need to examine each case within its project, still as we saw in the 4 examples above; the snag is generally more powerful than the cinch. Long live Murphy! That’s All Folks
