When {HEAD ~ the value} of {TAIL ~ the counter} reaches a prescribed value, which corresponds to the point at which substantially all the unburned particulates on the exhaust duct have been combusted, both the first and second counters are reset 
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When { HEAD ~ the value } of { TAIL ~ the counter } reaches a prescribed value , which corresponds to the point at which substantially all the unburned particulates on the exhaust duct have been combusted , both the first and second counters are reset
OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH