Note that I am so lazy that I don't investigate the signs of the coefficient so far. So only the absolute values of the coupling coefficients from the spactra are shown here...

The definition is

| TMS QPD PItch |   |  1           Y2P |   | Test Mass Pitch |

|                           | = |                      |   |                           |

| TMS QPD Yaw  |    |  P2Y       1    |   | Test Mass Yaw   |

If the coupling is just a geometrical rotation of the plain of the beam cross secrtion, at least the absolute value of Y2P and P2Y should be the same in theory. But such a condition was not fulfilled according to our measurements (for QPD1, it might be fulfilled, but for QPD2, it would be difficult).

Anyway, the numbers are (note again that they are all just absolute values!! The signs should be considered.):

• As previsouly mentined, even at the same QPD, P2Y for ITMX and ETMX differs, and so do for Y2P. It is hard to resolve this issue by a simple diag matrix. This would be an supportive evidence that this coupling is not the matter of electronics (leak to each segment or so) nor software (mis-wireing in the model or so). Maybe due to optical something...
• On QPD2, ETMX's Y2P is larger than 1, which is crazy... ITMX's P2Y as well.
• Stability: comparing to the previous trial (11832), the numbers on QPD2 are consistent, but those for QPD1 are slightly changed (about 1.1 times). Why?