Milestones are useful as a means of focusing on important events within a schedule. They can serve a number of purposes, such as:
- creating initial high level schedules during the identification phase of a project or programme;
- facilitating summary schedules for communication with stakeholders during the delivery phase;
- highlighting inter-dependencies between projects within a programme schedule.
When used as part of a network diagram, milestones are simply activities with zero duration.
These are entered into the logic of the diagram at the appropriate points. During critical path analysis their start dates, finish dates and float are calculated along with all the other activities but because they have zero duration they have no effect on the rest of the network.
At a programme level, it is useful to define milestones at points where there are interdependencies between projects within the programme. This provides a means of co-ordinating different projects based on actual progress.
It also provides a mechanism for summarising the schedule across multiple projects (or within large complex projects) and presenting a summary schedule that focuses purely on key events and doesn’t swamp the reader with too much detail.