NavList:

Yes, exactly. You pop that endcap off, and you can move the micrometer freely by loosening that screw. :)

I'll just note for anyone else who is following along that this is not a "necessary" adjustment. It doesn't affect the accuracy of sextant observations, and it's usually no more than cosmetic. The only real exception is when, just by chance, the micrometer alignment leaves the main arc pointer right in the middle, halfway between two angles, when the micrometer is reading zero. That could get confusing and maybe be a nuisance. In that case it's useful to get in there and rotate the initial position of the micrometer. Anything else is handled by the usual technique to reduce (or measure) the index error, and it's quite possible that you would never need to get at that screw under the endcap on the micrometer. :)

Frank Reed