Before you update a schedule for the first time, you should create a baseline plan. The simplest baseline plan is a complete copy, or snapshot, of the original schedule. This snapshot provides a target against which you can track a project’s cost, schedule, and performance. You can save a copy of the current project to use as the baseline or you can convert another project in the EPS hierarchy to a baseline for the current project.
To help categorize, or track, multiple baselines for a single project, you can assign each baseline a type that reflects its purpose, for example, initial planning baseline, What-if project baseline, customer sign-off, or midproject baseline.
Regardless of the number of baselines you store for a project, at any given time you can only select at most two baselines for use in making comparisons in P6. The project-level baseline is used for project/activity usage spreadsheets and profiles, as well as for earned value calculations.