Answer 2

The slopes on Mk2 correspond to about 1 turn in 512 MHz, in the same sense for both LL and RR. The slopes on Cm correspond to less than half a turn in the same sense for one polarization, and about a full turn in the opposite sense for the other. So the combination of errors, which will be solved entirely by correcting Cm, corresponds to magnitudes of <~1 ns and ~4 ns for the two polarizations, with opposite signs. The slopes, and hence the actual values, vary between spw, see the delay correction plot.