Hello, currently I'm testing frequency stability of an OCXO from NDK. The HP5370B is in the External Holdhoff & External Arm mode. From a pulse generator I apply a 10sec ON, 100ms OFF TTL signal to the External BNC jack, so I get a 10 sec long gate time for averaging jitter effects much quicker than the built-in 1sec maximum gate time. Additionally, I send the results via GPIB to the computer for the usual statistics on the data. Now I tried to replace the external pulse by software. I simulated the pulses from the generator by leaving the External jack open, or short circuit it, and by reversing the trigger slope on that jack (comands SE0 / SE1). This works quite fine, as the trigger LED operates, but the counter does not produce a result, obviously because the arming signal is reset directly by the GPIB commands. I also tried some other additional commands, but nothing works. Has anybody got an idea how to program the HP5370B for a gate time up to the maximum of 10sec? Dr. Frank Stellmach