Activities are generally identified by node numbers i.e. the number of events on either end of the activity arrow. Hence, it is essential to number events or nodes. The numbering should be carefully done so that the logical sequence is maintained. Fulkerson’s rule .

The numbering can be done in the following steps:-

1. There will be a single initial event in a network which has only arrows coming out of it. This event is given the number 1.
2. All the arrows coming out of event 1 are neglected. This provides us with one or more initial events. These events are numbered 2, 3 4 etc.
3. Again, neglect all the arrows coming out of these numbered events. A few more initial events will be created. These are also numbered similarly.
4. This operation is continued until the last event is reached and numbered.