The fit FWHM is 10.444kHz +-55Hz.
If we take the FSR from ELOG 9804, this implies an Xarm fineese of 380 +- 2.
Assuming an ITMX transmission of 1.4%, this means an Xarm loss of 240 +- 90ppm.
This is substatially lower than the ~500ppm I had measured via the unlocked/locked ASDC power method, but still pretty high.
Since we were able to get continuous frequency counter values into the digital system, I decided to give it a quick spin with a calibrated single arm ALS scan. This should be repeated when amplifiers are in place, because the Y IR beatnote is wandering around in a way I don't trust and I'm not sure if the frequency counters have good absolute calibration...
Neverthess, I did a 5 minute scan through the Xarm, and fit it nicely to a lorentzian peak.