The two principal modes of operation of universal counter timer instruments, such as
the HP5345A, are frequency measurement by counting events, such as positive zero
crossings of the signal with unknown frequency over the duration of an accurately
determined gate window. The duration of the gate window is determined by logic
circuits which count a preset number of internal master clock cycles. The gate dwell
can be set in the range 1000 s–100 ns in the HP5345A counter.