The SR620 measures time interval, frequency, pulse-width, rise and fall time, period, phase and events. Time intervals are measured with 25 ps rms resolution, making the SR620 one of the highest resolution counters available. Frequency is measured from 0.001 Hz to 1.3 GHz, and a choice of gates ranging from 1 period to 500 seconds are provided. The SR620 delivers up to 11 digits of frequency resolution in a 1 second measurement. It"s suitable for measurement applications ranging from short-term phase locked loop jitter, to long-term drift of atomic clocks. All measurement modes are supported by a wide variety of flexible arming and triggering options