Construction Project Management
Planning & Scheduling
Bar Charts
Building a CPM Schedule
Networks & Logic
CPM Scheduling
Logic Relationships & Precedence Networks
Progress Updating

Lag & Lead Time

[Whiteboard session] Here's a thorough explanation of lag and lead times and how to use them, along with an example.

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So, before we move to the next lesson, which is CPM calculations, we have one more thing to cover which is lags and leads.

What is a lag?

A lag is defined as a minimum waiting period between the finish of an activity and the start of its successor. So, they are done in sequence but not in direct sequence. There is a waiting period between them.

We use also the term lead which is a negative lag. So, in the English language or linguistically, lags and leads are like after and before. When you think of a lag, it's after. When you think of a lead it's before.

And as I mentioned before, one of the advantages of node networks that they can accommodate those lags and leads. Unlike their predecessors, the arrow networks, they cannot.

And let's take an example. If I put three days here and a two days here for example. That means activity D cannot start until at least three days after the completion of A. Activity E cannot start until at least two days after the completion of D. If we make this minus two days, we converted to a lead means activity E cannot start until at most, two days before the completion of the D.

Honestly, I don't use leads in my own scheduling. There are people who use them. Lags and leads will be used a lot more in precedence diagrams when we have overlapping activities with a start-to-start and finish-...

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