In the embodiment of FIG 3, if the first number of shock events detected at {HEAD ~ block} 40 does not exceed the upper event threshold , or if 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 { HEAD ~ block } 40 does not exceed the upper event threshold , or if 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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