Now that the camera is up and running again, a series of exposures have been taken to test the bias field.
Below is the old and new compared, and the difference in percent:
The bias level has changed by 1.3% or so, and the slope of the new field is different from the old - there is also some, smaller, change in curvature. The change in mean level is not so important since we scale the superbias to the current bias mean value anyway, but the change in slope is important. The relative level from up-slope to down-slope is something like 0.1% which is the adopted science goal for our project.
Further testing of the bias field will be performed as we proceed and if the above pattern is stable we shall simply start using a new superbias for currently acquired science frames. If studies show that the bias goes up and down and changes slope willy-nilly, as it were, then we have more to worry about!