In the Trenches with Microsoft® Office Project 2007

Managing Slack

Tasks that appear on the critical path are called critical tasks. By default, Project 2007 defines critical tasks as tasks without slack (also called float). Project calculates a task’s slack by calculating the difference between early finish and late finish dates; when these two dates are the same, the difference is zero, the task has no slack, and Project identifies the task as a critical task.

When a task has slack, you can afford to delay the task up to the amount of slack it has without placing the task on the critical path of your project. Generally speaking, if you delay a task that has slack, you won’t delay your project unless you delay the task beyond the amount of slack it has and don’t make up for this delay elsewhere. ...