NavList:

You wrote<Unfortunately the instrument is in error by about 15 degrees.>

If you set the reading to about 45 degrees and look in a direction from the arc to the axis on which the "mirror" rotates, you will see an Allen screw that locks the mirror on the axis. Slacken the screw and rotate the mirror about the axis to make the correction. It is also just do-able from the zero end of the scale with a key doctored so that the business end is about 8 mm long. This is more convenient (but more difficult to manipulate), as one can then use a horizon and known height of eye. Alternatively, you could borrow a dumpy or tilting level focussed at infinity and set level with a light shining into the eyepiece. You then look through the sextant at the objective end of the level and set the crosswires (if you can see them) at the centre of the bubble. Adjustments like this are much easier if the sextant is held still on a tripod. Just behind the bubble unit is a hole tapped 1/4 inch Whitworth (it may be UNC, which is nearly the same)so a camera tripod can be used.

Bill Morris
Pukenui
New Zealand
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