[gautam, johannes]

We let the PSL shutter closed overnight and observed the POXDC, POYDC and ASDC offsets. While POY has small fluctuations compared to the signal level, POX is worse off, and the drifts we observed live in the DC reading are in the same ballpark as the offset fluctuations. The POXDC level also unexpectedly increased suddenly without the PSL shutter being opened, which we can't explain. The data we took using POXDC cannot be trusted.

Even the ASDC occasionally shows some fluctuations, which is concerning because the change in value rivals the difference between locked and misaligned state. It turns out that the green shutters were left open, but that should not really affect the detectors in question.

We obtained loss numbers by measuring the arm reflections on the ASDC port instead. LSCoffsets was run before the data-taking run. For each arm we misaligned the respective other ITM to the point that moving it no longer had an impact on the ASDC reading. By taking a few quick data points we conclude the following numbers:

XARM: 247 ppm +/- 12 ppm
YARM: 285 ppm +/- 13 ppm

This is not in good agreement with the POYDC value. The script is currently running for the YARM for better statistics, which will take a couple hours.

ITMX is misaligned for the purpose of this measurement, with the original values saved.

GV edit 5Oct2016: Forgot to mention here that Johannes marked the spot positions on the ITMs and ETMs (as viewed on the QUAD in the control room) with a sharpie to reflect the current "well aligned" state.