During {TAIL ~ reversal} {HEAD ~ the servo system} which is driven into saturation senses the occurrence of zero motion of the drive mechanism and reverses the direction of energization of the electromagnetic drive 
During
During { TAIL ~ reversal } { HEAD ~ the servo system } which is driven into saturation senses the occurrence of zero motion of the drive mechanism and reverses the direction of energization of the electromagnetic drive
REL TAIL TAIL TAIL TAIL TAIL HEAD HEAD HEAD HEAD HEAD HEAD HEAD 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