The conventions used in a PERT are as follows. In the first version that is prepared, the Project Manager should number the events sequentially in multiple’s of 10s to allow insertion of events if required in between at a later stage. Two consecutive events are connected by activities represented by arrows. The events are represented in a logical sequence and no activity can commence till the preceding event is finished. The Project Manager or Planner decides which milestones constitute the events and their sequence. It may also have multiple pages with sub tasks.
The terminologies used are explained as follows. An event is a point that symbolizes the start or completion of one or more tasks. It consumes no time and resources. It is reached when all the activities preceding it are completed. An event may have predecessor (preceding event) or successor (succeeding event).
The predecessor and successor events may be outcome of one or more activity and has no intervening events. An activity is the actual performance of the task and uses time and resources. Implicitly it is the time, effort and resources required to move from one event to another. An activity can only complete if the event preceding it has occurred.
Optimistic time (O) is the minimum possible time required to complete a task under the theory that everything proceeds better than normal, Pessimistic time (P) is the maximum