Now, assume that the local factor of Activity 2 is reduced to just 0.7. This implies that the exact output value of the node becomes 19.0. That is, Activity 2 is finished on January 19. However, this is also the finish date of its predecessor, Activity 1. Hence, by the usual rule, we get that the duration of Activity 2 is zero days.

The question is: Which date should be displayed in the input field? If we use the day after the finish date of Activity 1, we get an input date that is one day later than the output date. Obviously, this does not make much sense. Instead, as a convention, for every date node with duration zero, we display the finish date of its predecessors in the input field. In the context of project scheduling, such date nodes are usually referred to as “milestones”.

Strictly speaking with an actual local value of 0.7, Activity 2 is not a “real” milestone. However, because of the rules we apply, Activity 2 appears to have zero duration, and this is what matters here.

It is interesting to observe that by increasing the local factor of Activity 2 to 0.8, its duration becomes 1 day. If so, the displayed input and output dates are switched to January 20.