Peforming some calibration measurements in the past weekend, I noticed that the red TRX and TRY QPDs had some dark offsets which were not quite cancelled. In this morning, since the interferometer was down, I adjusted the dark offset in each segment of all four qpds (ASC-X_TR_A and , and ASC-Y_TR_A and B). Subsequently I adjusted the LSC-TR offsets which receives the sum signals from these qpds -- the offsets are now zero as expected.