R&D Report 1970-16 : Field-store standards conversion: Servo-control of the field delay R.E. Davies A servo-control system is described which maintains the duration of a field delay equal to the field duration of the applied television signal. Errors in delay are corrected by binary-related lengths of coaxial cable which are switched into or out of circuit, as required. Since the range of control is insufficient using practical lengths of cable, several quartz delays are also included to accommodate larger errors. Delay errors are detected by comparing the timing of line synchronising pulses at the input and output of the delay and adjustments are made in steps of 9 ns.