You can use the assign baselines feature to designate the current project or an existing baseline as the project, primary, secondary, or tertiary baseline. The project baseline or primary baseline can be designated as the project to use when calculating earned value
Open the project for which you want to select a project baseline. Go to Menu bar, Choose Project, Assign Baselines.
The primary, secondary, and tertiary baselines are user-defined baselines used to compare projects.
In the Project field: select the project to which you want to assign a project baseline.