Data Type Duration (duration field: A type of field whose content is expressed as a duration of time. Examples include the Work, Duration, and Delay fields. A duration field includes the duration unit, such as hour, day, or week.)
Entry Type Calculated (calculated field: A field in which the value is determined by Project based on information in other fields. Project may recalculate the value automatically or when you specify, depending on your choice of calculation settings.)
Description The Free Slack field contains the amount of time that a task can be delayed without delaying any successor (successor: A task that cannot start or finish until another task starts or finishes.) tasks. If the task has no successors, free slack is the amount of time that a task can be delayed without delaying the entire project's finish date.
How Calculated If the task has no successor tasks, free slack is the same as total slack. Microsoft Office Project bases its calculations of free slack on comparisons of the dates in the Early Start, Early Finish, Late Start, and Late Finish fields for the task, which in turn take into account the dates for any successor tasks.
Best Uses Use the Free Slack field to determine whether a task has any time available for a delay. This can be useful if a resource needs more time on a task, or if you want to assign a resource to another task. You can also use the Free Slack field to determine how to recover a schedule that's slipping.
Example You are reviewing the schedule and want to see if there is any free slack on tasks. You add the Free Slack field to the Task Sheet view to see if a delay on tasks with free slack will affect any other tasks.