RE: what defines the baseline?
Hi Alex
The baseline is a snapshot of your project created when you go to Tools > Tracking > Baselines and choose "save baseline"
Project stores your duration, start, finish, cost and work values for your tasks so that later on you can compare your baseline snapshot against your current position.
You can view this information by switching to the tracking gantt view.
I hope this is helpful - do let us know if you have any further questions.
Kind regards,
Andrew