NavList:

I used to use an astrocompass to measure the deviation on sailboats and to adjust the compasses. I temporally mounted the astrocompass on the cabin top by first mounting it on a board that I could slide up against the edge of the the hatch cover track to get its lubber line aligned with with the boat's keel, this usually came very close, and then a check by measuring the offset from the keel line. A little computation to set it up and then changing the LHA one degree every four minutes made it easy to determine the true heading. Apply variation and, voila. Done in smooth water in the harbor took less than half an hour.
gl