From the course: Project Management Foundations: Schedules

Handle lag in dependencies - Microsoft Project Tutorial

From the course: Project Management Foundations: Schedules

Handle lag in dependencies

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- [Instructor] Sometimes, there's a lag between activities that means the successor doesn't start immediately after the predecessor finishes. For example, reviewing the manuscript can't finish until writing the manuscript is complete. What's more, the review finishes a few days after the manuscript is done because the reviewers need time to look over the last few chapters. One way to model a delay like this is to add the lag to the dependency between the tasks. Most scheduling tools can do this. In this example, suppose the reviewers need five days to complete their review after they receive the last few chapters. Add a five-day lag to the link, and the review activity is scheduled to finish five days after the manuscript is done. Lag can also represent delays that don't involve work, like the time concrete needs to cure. You could add a lag between pouring a foundation and framing the first floor to represent that curing time. Be sure to add a note to your schedule explaining the reason for any lag you add. You can't record progress on lag the way you can with an activity. When there is effort involved, here's how to reflect lag so you can record and monitor progress. Say you have to wait 10 days to get your printed training guides from the printer. Instead of adding lag to a dependency, you can add a new activity called print training guides with a duration of 10 days. When you link this activity to the milestones in the example, they are now 10 days apart, and it's easy to see what's being done during that time. If the printer emails progress updates, you can update the activity with that information. Don't use lag to represent buffers between activities. For instance, to provide time in case risk events occur. If you use lag in this way, you'll have to manually adjust the lag to reflect changes. Some scheduling tools let you create negative lag, also called lead, between activities. Instead of delaying the successor, negative lag overlaps the two activities. Negative lag is a big no-no in scheduling because it schedules the successor's start based on the predecessor's forecast finish date. And, sadly, there's no way to know for certain when the predecessor is going to finish. Here's a simple example of the problem negative lag can cause. Suppose you have a two-week writing activity and a two-week reviewing activity. You use lag of minus eight to overlap them by eight days. If the review goes faster than the writing, the review would finish before the writing, which doesn't make sense. What would happen in the real world is that the reviewers would have to stop and wait until there was more to review. Lag does have a place in scheduling, but you won't need it too often.

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