Leads and lags
“Leads and Lags” is a tool/technique for the process “Sequence Activities”.
A lead is the amount of time whereby a successor activity can be advanced with respect to a predecessor activity. For example, on a project to construct a new office building, the landscaping could be scheduled to start two weeks prior to the scheduled punch list completion. This would be shown as a finish-to-start with a two-week lead as shown in Figure 6-10. Lead is often represented as a negative value for lag in scheduling software.
Complete Punch List Write Draft Landscape Building Lot Edit Draft FS ? 2 Weeks (Lead) SS ? 15 Days (Lag) Figure 6-10. Examples of Lead and Lag A lag is the amount of time whereby a successor activity will be delayed with respect to a predecessor activity.
For example, a technical writing team may begin editing the draft of a large document 15 days after they begin writing it. This can be shown as a start-to-start relationship with a 15-day lag as shown in Figure 6-10. Lag can also be represented in project schedule network diagrams as shown in Figure 6-11 in the relationship between activities H and I, as indicated by the nomenclature SS+10 (start-to-start plus 10 days lag) even though offset is not shown relative to a timescale.
The project management team determines the dependencies that may require a lead or a lag to accurately define the logical relationship. The use of leads and lags should not replace schedule logic. Activities and their related assumptions should be documented.
“Leads and Lags” is a tool/technique for the process “Develop Schedule”.
Leads and lags are refinements applied during network analysis to develop a viable schedule by adjusting the start time of the successor activities. Leads are used in limited circumstances to advance a successor activity with respect to the predecessor activity, and lags are used in limited circumstances where processes require a set period of time to elapse between the predecessors and successors without work or resource impact.
“Leads and Lags” is a tool/technique for the process “Control Schedule”.
Adjusting leads and lags is applied during network analysis to find ways to bring project activities that are behind into alignment with the plan. For example, on a project to construct a new office building, the landscaping can be adjusted to start before the exterior work of the building is complete by increasing the lead time in the relationship. Or, a technical writing team can adjust the start of editing the draft of a large document immediately after the document is completed by eliminating or decreasing lag time.
This definition was found in the PMBOK V5
Go back to the Glossary or to the Mapping