A milestone is used to represent groups of activities or significant events or commitments in the project. A milestone chart shows a group of milestones in an organized way similar to a Gantt chart with one milestone per line vertically with a description on the left and the milestone located horizontally along a time scale showing when it occurs. Milestones differ from the bars in a Gantt chart in that they show only a single date and are usually depicted as a triangle instead of a bar (see MILESTONE CHART). Milestones can be shown in various colors depicting the status of the milestone. Milestones can also appear on Gantt charts; project management software supports the placement of milestones on Gantt charts and other project reports and displays generated by the software.
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In the early days of project management, project managers made up Gantt charts for their projects. These Gantt charts could be quite large when projects contained over one hundred activities. It was not practical for the project manager to duplicate the Gantt chart for her manager, and if the supervisor of the project managers had several project managers, it was not practical to display all of the projects’ Gantt charts unless there was quite a lot of wall space.
The milestone chart was devised to save space on the project managers’ supervisor’s walls. Each project manager collected related groups of activities in the project and assigned a milestone to each group. A milestone was placed on the project schedule representing the group. Another milestone was placed on the project managers’ supervisor’s milestone chart as well.
If there were changes in the schedule that affected the completion date of the milestone, the project manager had to visit the supervisor’s office and move the milestone. In all likelihood the project manager gave an explanation of the schedule slide at this time as well. Of course, this kind of explanation was not always the most pleasant sort of meeting.
Milestone schedules can be produced using today’s project management software. They are created simply by listing the milestones as activities and giving them a duration of zero. Since they are being created on a Gantt chart, the length of the Gantt schedule bar for the milestone would have a zero length and could not be seen. A triangle or another symbol is put on the chart instead. The symbol can be colored to show various statuses and conditions as needed.
If the milestones are mixed into the normal Gantt chart showing all of the activities involved in the project, the milestone chart can still be produced by simply selecting the activities that have a duration of zero and printing the milestone chart with these activities.
There is one risk in creating these milestone charts. The placement of the milestone on the time scale can be done two ways. One way is to simply assign a date constraint such as "Must Finish On" to the milestone. If any of the activities in the group is rescheduled and the milestone is not changed by hand, it will still show the original date and thus give the wrong information when the milestone chart is produced.
The second way of placing a milestone is to create a finish-start relationship with the activity in the group that has the latest early finish date. In this way the milestone will be rescheduled if this activity is rescheduled. Still, there is risk in this technique as well because it is possible that other activities in the group could be rescheduled without rescheduling the activity the milestone depends on.
If using milestone schedules, the best thing to do is to set up a finish-start relationship between all of the activities that can be delayed past the milestone and the milestone itself. In this way if any of the activities is rescheduled, the milestone will automatically be rescheduled as well.
A better method for summarizing project activities is the summary or hammock activity. This allows more automatic tracking of projects and also gives the start and finish dates for the group of activities.