With Hirata-san.

Summary: we assessed the height of the optic and chose a suitable position for the F1 keystone.

See pictures in the album BS Remedying work after O3.

• We set all the GAS filters to zero using the control system.
• We inspected the position of the RM screws with respect to the laser level that indicated the desired height of the optic.
• Then, we adjusted the position of the F1 GAS filter keystone in order to have the optic at the desired height. We did this by changing the setpoint of the control system: 572 counts, which corresponds to -400 um with the current temporary calibration factor and offset. The calibration factor and offset will change in the future, but the setpoint in units of counts should still be used.

There are observations:

• The BS recoil mass does not have scratch lines, so we use some vented screws as reference. We can't place a ruler either, so we need to rely on visual inspection in situ and analyze the pictures afterwards. These conditions likely increase the error in the measurement.
• According to the displacement of the left screw, we moved  the F1 keystone down by approximately 0.7 mm, which is a small amount given the reproducibility and error in the measurement. (See first and second pictures.)
• The height of both screws after the adjustment was close to the desired height. (The third picture shows the right screw after the adjustment.)
• The actuation required for this was around -24,000 counts, which is very large.
• T =  23.2 °C ondotori (T_O3GK = 23.0 °C).