NavList:

Dear Modris,

You wrote: The Russian article that you attached to your previous post is from the book of Krasovskii, The author of the book is Krasavcev (not Krasovskii).

You are right. I confused the name in my message. It is the same author and the same book.

I would like to ask you (or anybody who is competent) a question about  SNO-T. In the instruction it is printed: range of angles readings 140°, range of angles measurement 120°. Certificate data range is also only 0°-120°. 

I do not know the answers to: a) why did they make such a long arc; no other modern sextant that I know has such a long arc. It almost qualifies as a "pentant/quintant". b)  why do they say that it is usable for up to 120. But for the second question, I have some conjectures.

I tried once to do some Lunars at about 135 degrees, and obtained poor results (1' to 2' errors, this is not good for Lunars). The problem was that the index mirror looks too narrow under such angle; it is hard to keep Sun and Moon in the field of view.

But I was able to do  Lunars with reasonable results for up to 130 angles. I know that Lunars are not used for real world navigation nowadays, but there is another reason for measuring large angles: determination of horizontal angle between two objects whose position you know,  which is probably widely used for various purposes. And with angles >130 they must experience the same difficulty that I had with my Lunars.

 My SNO-M sextant also has similar angle values, but I can easily to take sights up to 135°.

Have you been able to obtain good results for Lunars with such angles ?

Alex.