means suitable for registering, from the end of the spark produced by the spark plug, the signals of {HEAD ~ the ion current} produced and detected in the secondary circuit of {TAIL ~ the device} of each cylinder whose piston is at the top dead centre  
means suitable for registering , from the end of the spark produced by the spark plug , the signals of { HEAD ~ the ion current } produced and detected in the secondary circuit of { TAIL ~ the device } of each cylinder whose piston is at the top dead centre
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH