Because of drift issues that we've been seeing in the BBSS, we've been looking into center of mass issues, and we are now looking at the lowest stage, M3, and the possibility that the stainless steel center insert (which was installed upside down) is causing pitch issues.

We wanted to go through and verify what the physical d4 value, aka the physical location of the prism-clamp breakoff point, is in our latest set of measurements we took at the end of October. We wanted to verify this just because when we were messing around with d4 back in early 2024 (75947, 76071), we never checked any measurements where we changed around d4 with the stage2 parameter correctly on, meaning that those d4 comparisons all plotted changes in the effective d's instead of the physical d's.

I've plotted a few parameter sets where the stage2 parameter is on so we can more properly compare them.

I've plotted:

• the current default parameter set, which has d4 = FDR = 0.5mm, as well as having d1 = FDR - 2.5mm
  • this parameter set had been decided by us to be the new default a while ago
• variations on the FDR parameter set, with d4 being the FDR d4 value shifted by +/- 0.5, 1.0, or 1.5mm. For these parameter sets, d1 is left as its original FDR value
• Our most recent measurements from October 31st, which was after all the M1 blade heights had been changed

Here are the plots. The zoomed L and P plots are the best for seeing the differences between the different parameters.

The Oct31 measurement seems to match best somewhere between d4 - 1.0mm and d4 - 0.5mm, so the value of  d4 that we have in our current set seems to still match pretty well.

It is interesting to see though the difference between the dark red and the yellow traces as compared to our latest measurement, since the only difference between those two is the d1 value. It looks like somewhere along while messing with the blade heights, we also moved away from the d1 = FDR - 2.5mm value and closer to the d1 value given in the FDR.