When the second number of {TAIL ~ shock events} exceeds {HEAD ~ the upper event threshold}, the shock threshold is increased 
When the second number of { TAIL ~ shock events } exceeds { HEAD ~ the upper event threshold } , the shock threshold is increased
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH