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 Start Slack field contains the duration between the Early Start and Late Start dates. The smaller of the start slack and finish slack amounts determines the amount of free slack (free slack: The amount of time that a task can be delayed without delaying its successor tasks. For a task without successors, free slack is the amount of time that the task can be delayed without delaying the finish date of the project.) available, that is, the amount of time a task can be delayed without affecting the start date of a successor task or the project finish date.
How Calculated Start slack is the duration that represents the difference between the early start and late start dates. The early start is the earliest date that a task could possibly start. Likewise, the Late Start field contains the latest date that a task can start without delaying the finish of the project. Microsoft Office Project calculates the start slack as follows:
Start Slack = Late Start - Early Start
Best Uses Add the Start Slack and Finish Slack fields to any task view when you want to review how free slack was calculated.
Example You are reviewing free slack in your schedule and want to see more details about how it was calculated. You add the Start Slack and Finish Slack fields to the task sheet and analyze the durations.
Remarks If a task has an actual start date and a deadline (deadline: A target date indicating when you want a task to be completed. If the deadline date passes and the task is not completed, Project displays an indicator.), the start slack is 0 and the finish slack is the difference between the task's finish date and deadline date.