What screw should I use to adjust sextant mirror?

Hello everybody,
I recently borrowed a Tamaya MS 833 sextant, and I would like to adjust index and horizon mirror positions. Please find attached a picture of the back of the index mirror. From the instruction manual it is unclear whether the screw that adjusts the perpendicularity error is the one circled in red or the one circled in green.

What do you guys think?

There is a good description of how to calibrate a sextant in Bowditch.

It’s the Red one.

1 Like

Yep the red one

1 Like

Thank you, but Bowditch does not say anything about this specific question

Thank you. What key should I use to adjust it? It looks like it should have a square hollow.

1 Like

If you haven’t seen this adjustments are on page 11.

sextant_e.pdf (tamaya-technics.com)

I have read those pages, and that is the part which is unclear: The line which starts from ‘C’ in the image on page 11 points to nowhere in the middle of the horizon mirror.

With regards to the Horizon mirror you can see the adjustment screws referenced as B and C in the Tamaya brochure. (In the brochure line “C” extended too far).


Thanks, see my previous post indeed.

Thank you. Do you know what is the size of the square in the key for the Tamaya MS 833 sextant? I have been looking for that key online, it appears to be a clock key, and it comes in different sizes, see for example here.

The size of the square for the Tamaya MS 833 is around 2mm (2 mm would be a 00 key), but I don’t have a calipers and it could be also 2,25 mm or 2,5 mm.

The proper wrench is supplied with the sextant – suggest ask Tamaya for a genuine one.

1 Like

Yes a 00 key should work.


1 Like