NavList:

Good day, Michael. Regarding the Mk IXA

I too have been chasing the cause of these wandering variations .  Two years worth of many hundreds of Observations, have  shown no detectable pattern or stability in the errors.

I have had the instrument completely  in pieces , both for knowledge and in the faint hope of identifying a possible cause, to no avail.

I've changed out a few  parts for replacements and even managed to track down a source of 'n-hexane' for the proper bubble fluid.

I now think that the likely cause, is minute instabilities in the seating security of the Index mirror.

Regards

Lawrie Elms