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glapook@PACBELL.NET wrote:

Attached is a copy of an english translation of the manual for the
SNO-T  russian sextant.

Two things of interest. First, there is a luminescent coating around the
magnifier for reading the scale that can be activated with a flashlight
and the glow makes it easy to read the sextant in the dark. I never knew
it was there.

Second, it describes a method of measuring the index error by bringing
the top and bottom edges of the sun together twice and then the average
of these readings will give you the index error. For example, assume no
index error and the semi-diameter is 15'. Bringing the upper limb of the
reflected image of the sun into conjunction with the lower limb of the
direct image should give you a reading of minus 30'. Then putting the
lower limb of the reflected image in conjunction with the upper limb of
the direct image should read plus 30'. The average of these reading is
zero, no I.E. If the  readings were minus 20' and plus 40' then the I.E.
would be plus 10' . This avoids using the horizon.


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