VVT Parameter question

I did search, and did check the tuning tool manual but didn't see a complete answer to my question.

Low, Med, and High Baro. Obviously they are pressure parameters but it is unclear to me what causes the transition from one table to the next.

Is this a reading that is taken from the MAP at start up so that the engine runs in an appropriate manner for the elevation?

OR

Are these three tables that dictate cam timing based on continual checks of the MAP during operation? Transitioning from table to table based on throttle position?

Thanks