J. Kissel, F. Clara

I'm yak shaving, but at the end of today's kLog series you'll understand how to execute Daniel's implicit plan in D0902810-v10 for moving cables around to make room for an incoming tip-tilt, aka HTTS, to eventually be named "PM1," i.e. Pop wfs steering Mirror 1.

In this kLog: I've labeled the U heights of SUS-R1.

SUS-R1 is an old iLIGO rack that was never labelled, but repurposed in aLIGO to house (mostly) HAM2 SUS satellite amps, i.e. the triples MC1, MC3, PRM, PR3, and the singles IM1, IM2, IM3, and IM4. (It also houses a CDS network switch, a PEM test panel, and a deprecated  / never used HAM2 and HAM3 ISI optical lever whitening chassis.)

In aLIGO, all U-slots in U42-ish height racks were "converted" to being labeled by industry standard with the top being U42, and the bottom being U1. These iLIGO racks don't have enough slots to populate all 42 U-height slots, so the compromise is to *draw* 42 U-heights, but "never use" U1.

The last bit of the story: the drawing that governs the content of these racks is D0902810. However, when the aLIGO field racks were populated with stuff, 
    (a) The sites made a custom non-standard 3.25-ish U-height "craddle" to hold the non-rack-mountable UK satamps.
    (b) that drawing did not cover the layout of the field racks, so each sites kinda "did what they wanted."
The issue (b) was been rectified by 2023 as Louis Sanchez and I brought D0902810 up to -v9, see IIET:5097.

So, that's why the U-height labels don't awesomely line up with the chassis that are installed.

See 
- Screenshot of depiction of the rack in page 13 D0902810-v10, with the rack labeled "top down" from U42 at the top and U41 at the bottom (even though the H1 "as-built" version of this design doesn't have a U1).
- single "before" picture
- The rest of the attachment: pictures of the labels.