During {TAIL ~ reversal} 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 {HEAD ~ the electromagnetic drive} 
During { TAIL ~ reversal } 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 { HEAD ~ the electromagnetic drive }
OTH 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 HEAD HEAD HEAD HEAD HEAD HEAD HEAD