A tachometer module 81 generates {HEAD ~ a collimated light beam} which passes through the encoder disk 80 to a photodetector array which puts out {TAIL ~ electrical signals} in quadrature relationship indicative of both velocity and direction of movement of the tape 20 
A tachometer module 81 generates { HEAD ~ a collimated light beam } which passes through the encoder disk 80 to a photodetector array which puts out { TAIL ~ electrical signals } in quadrature relationship indicative of both velocity and direction of movement of the tape 20
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH 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 OTH OTH OTH