Hi whobrokeit,
the baseline is counted based polled values over a period of time. The length of that period is 7 days by default and can be changed on SAM settings->Data&Database settings page.
You can count these values manually by using 'Use Latest Baseline Thresholds' button next to a selected threshold. In this case you can get values which can be based on shorter period of time.
Or it could be set automatically after the period of time during nightly maintenance. This is done by application of ${USE_BASELINE} formula.
For counting warning and critical values are used following formulas:
warning threshold: Mean +- 2xStandard deviation
critical threshold: Mean +- 3xStandard deviation
Counted thresholds remains the same until you change it manually or automatically in the same manner as first time.