Baselines
Baselines provide a "snapshot" of a project status by storing a complete set of project data for a specific point in time.
Open Plan allows you to store multiple project baselines so that you can maintain a historical record of changes over the life of a project.
Use the Baselines option to display the Baseline dialog box where you can select a baseline from a list of baselines already included in the project file. You can also add, update existing, or delete baselines from the Baseline dialog box.