In the embodiment of FIG 3, if the first number of shock events detected at block 40 does not exceed the upper event threshold , or if {HEAD ~ the second number} of {TAIL ~ shock events} does not exceed the upper event threshold , then the detected number of shock events is compared to a lower event threshold  
In the embodiment of FIG 3 , if the first number of shock events detected at block 40 does not exceed the upper event threshold , or if { HEAD ~ the second number } of { TAIL ~ shock events } does not exceed the upper event threshold , then the detected number of shock events is compared to a lower event threshold
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