Wires 46 of the readhead 29 are plugged into {HEAD ~ a connector} 47 that is electrically connected to {TAIL ~ a pair} of go/no go LEDs 48, via an amplifying and comparator circuit  
is electrically connected to
Wires 46 of the readhead 29 are plugged into { HEAD ~ a connector } 47 that is electrically connected to { TAIL ~ a pair } of go / no go LEDs 48 , via an amplifying and comparator circuit
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH