Today was mostly devoted to finishing the alignment process Kyle started in the optics box. We fixed our mechanical overconstraint as mentioned yesterday, but we were still getting unreliable results from our lens alignment procedure. We finally realized that we actually had to rethink part of the process: we were trying to align to something that had too many interdependent parameters. Once we picked a different reference point to align to, the process went more smoothly. Kyle also installed and aligned the polarizing grid in the optics box, so now all of the 1 Kelvin optics are done.
In the meantime, Jeff continued to work on the cold wiring and assembly of the half-wave-plate assembly. One issue that came up was trying to figure out how best to understand the position of the HWP relative to the rest of the cryostat. The HWP rotates, but at any given point in time you need to know its orientation to some known coordinate system so you can figure out the polarization on the sky. It turns out that this isn't a trivial task, but we came up with a procedure for measuring the position of the HWP assembly relative to the outside of the cryostat that should work. We spent a lot of time verifying that this procedure was robust by making many test measurements and checking their repeatability.
Last, I appear to have hurt myself. I must have done something to my ankle while running the past couple of days (Friday and Sunday) and I'm now walking around (slowly) with a noticeable limp. I'm sure it wasn't helped by having to climb up and down ladders in order to make measurements. Hopefully with ice and compression, it will get better by itself in a couple of days...fingers crossed!