NavList:

Dear David,

thanks a lot for the description and illustration of the backlash-reducing arrangement. It's really clever!

However, if I'm not mistaken, since the index arm holding the vernier scale is connected firmly to the "mirror" (glass, in reality), by which I mean that there are no gears in between, there cannot be any backlash-related error between the reading of the vernier and the image you observe when looking through the instrument.

Pencil marks on the drum can be affected but I don't use this feature of the sextant.

Is my reasoning correct? If so, it appears I'll have to look elsewhere for the source of the error.

Matus