Critical path analysis

The various logic links referred to above can have periods of times assigned to them, to dictate a period between the start and/or finish of one activity and the start and/or finish of the succeeding activity. These are generally referred to as leads and lags.

Figure 5: Lead

The example above shows a start-to-start relationship meaning that activity B cannot start until activity A has started. In this case a lead-time of 2 days has been assigned to the logic link meaning that activity B cannot start until 2 days after activity A has started. This is referred to as a lead.

Figure 6: Lag

Similarly a lag of 2 days has been assigned to the finish-to-finish logic link meaning that activity B cannot finish until 2 days after activity A has finished. This is referred to as a lag.

Figure 7: Negative lag

Negative times can be assigned to the logic and in the above example activity B can start 3 days before A finishes.