J. Kissel, D. Tuyenbayev, J. Betzwieser, S. Kandhasamy

We recently found out LHO has not included the LSC Output matrix in their matlab model of the DARM loop (see LHO aLOG 21601), and this resulted in a discrepant phase in the calculation of the time-dependent parameters. Independently, of the few hardware injections we've managed to test thus far, there remains a minus sign found in the H1 reconstruction (LHO aLOG 21616). Finally, Maddie has found that the sign of DELTAL_CTRL is different between the two observatories (no aLOG yet).

The messages: 
- We have found that CAL-CS *also* does *not* include this LSC OUTPUT MATRIX -1. We think this is an error, yet somehow the CAL_DELTAL_EXTERNAL is still showing sensible results, and we don't understand why.

- We believe this explains the missing sign in the inverse actuation filter. LHO has been inverting the DARM matlab model's version of the actuation function, which did *not* include the LSC output matrix, i.e. a -1, and hardware injections are injected upstream of this output matrix in the DARM path.

- We don't understand what we see when the CAL-CS installations comparing between sites (LHO does NOT account the output matrix, where LLO does, and both sites produce sensible DELTAL EXTERNAL ASDs).

Attached are screenshots of the CAL-CS MEDM screen, the replica of the LSC output matrix, and its actual counterpart in from the LSC overview screen, to prove to myself what is true. 

The path forward: 
- A sanity check: Take two transfer functions, DELTAL_CTRL to DELTAL_EXT and DELTA_RESIDUAL to DELTAL_EXTERNAL. Export them into matlab, add them and subtract them. Check if DELTAL_EXTERNAL would even notice if A was + or -. Our intuition says "yes, it should make some nasty bump or zero in the calibrated ASD."
- Make a sign table like LLO has in LHO aLOG 20587.
- Plot comparisons between both models, and make sure it makes sense.
- Figure out how to handle "the feedback minus sign" convention, to confirm that we're both obeying what's shown in LHO aLOG 21601