I estimated the beam positions of MIF IR and XPcal path 1/2 on ETMX surface during O4a based on Tcam images we took on the maintenance days.

In the whole O4a period, the results were as follows.

Main IR: $x=4.6\pm1.3, y=2.5 \pm 1.0$

XPcal path 1: $x=2.71 \pm 0.97, y=70.30 \pm 1.0$

XPcal path 1: $x=2.3 \pm 1.4, y=-60.2 \pm 1.0$

From these values, we will calculate the effect on Pcal and the uncertainty.

Note:

• The origin point is at the center of the HR surface.
• +x axis is negative y-arm direction of the interferometer.
• +y axis is the vertical up direction.
• Unit is mm.

Detailed report: link