If your project plan consists purely of tasks, or just tasks and phases, it may not be apparent when you’ve completed a major step. To mark the completion or beginning of significant sections of your project, you can add milestones.
In Microsoft Project, a milestone is indicated by a task with zero duration. So, your first step in adding a milestone is to enter it in the Task Name field. When you enter a duration of zero days for the task, Microsoft Project displays a distinctive diamond-shaped milestone symbol at the start of that day on the Gantt Chart.
Add a milestone to the end of a phase or to mark a point in the project when you must deliver something to a supervisor or a client (such as a report, a product, or a service) that’s due before the project ends.
To enter a milestone
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or press ENTER.