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Dear list members,

Could you make the following experiment for me:
determine the backlash of your sextant.
This is very simple.

1. Choose a weak star. (As weak as you can see with your naked eye).
2. Point your sextant at it (with 0 setting) and align the reflected
image  of the star with the straight image of the same star,
as you do in
determining your index error
(or IC).
The two images will not be perfectly coinciding if your
horizon mirror is not perfectly parallel to the index mirror,
this is a "side error", and it does not matter in this experiment.
3. When the two images of the star coincide (or are "on the same
horizontal level"
if you have a slight parallelism error),
4. Rotate your screw CLOCKWISE a little bit
to break the alignment, and then ANTI-CLOCKWISE until the lighnment is
perfect.
5. Read the scale and record.
6. Rotate your screw ANTI-CLOCKWISE a little to break the alignemt,
then then CLOCKWISE until the alighnemt is perfect, and
7. Read and record the the reading.
8. E-mail these two readings to me or to the list,
together with the brand, and year made (and any other detail you wish to
add about your sextant).

Thanks in advance.
Alex.

   

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