[Aidan]

Summary:

Attached image shows HWS ETMX point absorber measurement from 2018. Coordinates of the point = [-25mm, +50mm] +/- [8mm, 8mm] as viewed from the front of the optic.

Details

In order to assist with point absorber analysis for O4, I attempted to orient the HWS image from H1 ETMX. To do this, I assume the imaging system was the same as LLO and the sign of the axes was the same for the OPTIC coordinates and HWS coordinates (as is the case in that setup).

Under that assumption, there is a point in the upper left quadrant of the optic around [-25mm, +50mm]. I estimate approximately +/-3mm uncertainty in the position of this point due to random noise sources. To locate the center of the OPTIC coordinate system in the HWS coordinate system, I used an image of the HWS intensity pattern. The circular array of points sees an aperture of the  TMS Telescope SSTL Baffle Plate, D1102297  baffle in the image (see LLO aLOG 54473). This circular aperture appeared to be offset by 5mm in both X and Y directions (see attached image), but the direction of that offset is not clear. So I'm adding +5mm as a systematic error. Direct sum of random and systematic errors yields approximately +/-8mm uncertainty in the location of the point on the ETMX surface.