Understandng the output from show sipd sessions

I wonder if someone could clarify exactly what each value means in the results of a "show sipd sessions". So for example with the below active seems fairly self explanatory as the current active number of SIP sessions but what would high and total be? Lifetime I assume is total sessions since the SBC was last restarted.

Session Stats           -- Period -- ----- --- Lifetime --------

            Active   High  Total   Total  PerMax  High

The reason I ask this is I was asked to say what the peak SBC sessions was on an SBC and I had always thought the High in Period represented the peak sessions seen on the SBC since previous reboot but I noticed if I kept issuing "show sipd sessions" sometimes the High value would reduce so this made me question if my understanding of that value is correct as I would not expect a peak value to ever reduce unless the SBC is restarted.