tvb@LeapSecond.com said: > No, not narrow pulses. Do not use the trailing edge of a 1PPS. This is more > about 1 Hz from a stable frequency standard, not 1PPS from a noisy GPS > receiver. I think we are discussing two different things. Your setup would work if the pulse-under-test is drifting. Mine won't. I was trying to inquire about the stability of the pulse width. If your reference pulse is known to be stable and is wide enough, you can use the trailing edge to stop a TIC and the normal/leading edge of your to-be-measured pulse to start the TIC. That's just a hack to displace an edge far enough so that there is no sign reversal on the time between two pulses when one of them wanders around. It doesn't require any extra gear. Your suggestion requires a wide pulse and some software. None of my GPSDOs have a wide pulse. I assume one of your PIC options would do what is needed if run from the 10 MHz which my GPSDOs do put out. (Do you have a 15 MHz option?) -- These are my opinions. I hate spam.