Attached is a mode scan of the y-arm cavity (ring heater on). Both the DARM offset and the frequency counter are calibrated in mircons for the y-arm.

- Our ALS-DIFF calibration is a factor of 3 off - I needed about 3 micron per count from H1:ALS-C_DIFF_PLL_CTRL_OUT, which advertises to be calibrated in micron.

- The expected transverse mode spacing for the y-arm is 8.5 kHz (Ritm=2307m Retm=2238.9m, The ITM is also currently being heated weigh the ring heater.).  The mode scan measurement is consistent with 8.5kHz, with an or or of about 500Hz.

- The problem with that is that the 45MHz sideband is 16261Hz  off the resonance, bringing the 20mode nominally to 738Hz .

- We suspect the the first side we tired to approach from (left side on the COMM offset slider) was contaminated by this mode. We're now trying the other side.