[time-nuts] Time Interval Counter(?) for high-precision watch measurement

[Raven L]

Hello time nuts and greetings from the 10^-10 world of high precision
wristwatches.

I'm trying to set up a lab for automated watch measurement. I have a basic
GPSDO with a PPS and a 10MHz output. I use an inductive sensor to pick up
the signal from the motor inside the watch.

I've been using a basic digital oscilloscope to measure the interval
between the PPS and the watch signal.  The signal from the watch has a
total rise time of about 10us to 40us, varying by watch, and rises a few
volts above a noise floor of about 50mV. The oscilloscope does a
serviceable job but doesn't allow automated measurements and can't be
driven by an external timebase. My goal is to make measurements with a
precision of about 10us, with a goal of ultimately pinning down a rate to
better than 0.001 seconds per year (initial testing shows this is what I
need to resolve the effect of tipover on AT-cut MHz-range quartz crystals).

Are there specific time interval counters or frequency counters that would
make this easier?  I've been looking at the SR620 as a candidate, which
appears to be available used for around 2k USD, but wouldn't be surprised
to learn if there was something that was a meaningfully better fit. Thanks!