When the PM window is first displayed for the specified project, the activities are listed in the order in which they are defined in the Activity data set. The activity numbers displayed in the Job Nbr. column correspond to this same order. Even if the activities are rearranged, either by moving selected activities or by sorting, these numbers do not change. Likewise, no renumbering takes place automatically if activities are deleted from the project.

You can use the Renumber selection in the Project menu (Figure 5.32) to reassign consecutive numbers to the activities, starting from the first activity displayed.

When you close the PM window, saving all the activity information to the Schedule data set, the activities are numbered according to the order in which they were displayed at the end of the editing session. In other words, the Close action implicitly invokes the Renumber command on the project activities. These activity numbers are, in fact, saved as the values of the ACTID variable (see Schedule Data Set).