A baseline is a snapshot of task plan data that can be used to compare the original project with the current project. The initial baseline should be used to represent the original, approved scope of a task plan, including its costs, dates, durations, labor assignments, and so on. It should be set after the task plan has been created, but before any work on a task plan is started.

As a task plan progresses, changes to the original scope, resource allocation, and budget will affect the original estimates. You can use add new baselines, with which comparisions between original and actual data can be made. For task plans that diverge greatly from the original, it may help to create a new task plan with new targets and a new baseline.

A task plan can have up to eleven saved baselines; each baseline saves cost, work, start, finish, and duration values. A baseline can be set to one or more tasks in a task plan or for an entire task plan.