Although not very well known in the West, the Russian CHO-T (SNO-T) is the last polished design in nautical sextants.  Actually, very close to a quintant (measuring up to 140 degrees) it enhances all of the important features and addresses all of the shortfalls of past designs.  Its very existence is an unlikelihood in both purpose and timeliness since there was almost no rhyme or reason for its development.

In the mid-1970s, the US and Russia had global positioning satellite systems in the works.  The concept had been proven by both countries, the R&D was well underway and the only thing left was for one or both countries to start building.

For whatever reason, right around that time, the Russians not only decided they needed a newly designed sextant, but that it also had to be better than the East German Freiberger which had already proven itself equal to the West German Plath.  Perhaps they were anticipating the East Germans soon joining the West, but it made no sense with GPS right around the corner, that the Russians would have produced anything more than a cheap knockoff of the Freiberger as a temporary stand-in.  This is not at all what they did.  But why they decided to pour their hearts into designing this instrument is most likely just another one of those many Russian secrets.

W. J. Morris, author of The Marine Sextant, refers to the CHO-T sextant as "(a) very high-quality sextant, possibly the best ever made."  Of course, in the same breath, he humorously condemns the box for the "let down" that it was: https://sextantbook.com/category/the-ussr-sno-t-sextant/.  But here again, this is what might have been expected of the Russians in the 1970s. They wanted the absolute best in terms of performance and were ready to forego the frills.  The box is painted grey on the outside, with a garish yellow inside. Although functional, it's unattractive.  It is, in fact, so very Soviet.

In his 2010 publication, Bill Morris devotes much writing to the CHO-T, perhaps more than justified relative to the rarity of this instrument outside of former Soviet countries. There aren't that many out there for Westerners to get a hold of.  And although he does intimate as to why this is possibly the best sextant ever made, I will now elaborate.

First of all, it's the right color.

Whoever it was that decided that a sextant, especially an aluminum one, should be painted black, should have been tarred, feathered and run out of town before he could wreak havoc on an entire industry.  A sextant should reflect the sun's energy, not absorb it!  No one can appreciate this more than a person trying to clear the lunar distance between the sun and the moon only to witness the moon stop and then suddenly turn and move in the opposite direction.  This is not the heavens reversing themselves.  This is simply another black sextant twisting in the breeze.  The CHO-T sextant is painted silver.  The T in CHO-T stands for tropicalized.  It took Plath almost until the turn of the century to accept this reality.

Unlike the 7 threads on the worm of a Plath and most others, the CHO-T has a worm with 15 threads.  But more importantly, unlike the fixed pressure of the worm against the rack, the CHO-T, much like the Freiberger, has a very sophisticated and highly adjustable pressure system.  These are two very important features in achieving the silky smooth (near zero backlash) micrometer drum motion needed to achieve the 6 seconds of arc accuracy which this instrument boasts.

The extremely close tolerance of the index journal, with its diameter of about 3 to 4 times that of most other designs, greatly contributes to the stability and rigidity of the index arm movement.

Reducing the weight of a sextant is important to the practical accuracy of the instrument.  However, in most cases, a reduction in weight is often achieved at the sacrifice of rigidity.  Not so with the CHO-T.

As Bill Morris points out in his highly authoritative treatise, the CHO-T sextant frame scored the best in terms of weight/rigidity of the 9 sextants tested of both bronze and aluminum alloy.  By the way, if you are interested in owning any of the top-priced sextant models, you definitely want to invest in his book.  It's totally devoted to renovation, maintenance and adjustment and is much more in-depth than his website info.

Unlike the back-silvered index mirrors of all other models, the CHO-T index mirror is a first-surface reflector.  This eliminates the high-angle, double-bounce refraction error and reduces the star glare that all other sextants suffer.

The micrometer drum does not have a vernier scale.  None is needed.  The CHO-T makes use of a fully adjustable magnifier loupe that services both the main and micrometer scales.  When you look through the loupe at the micrometer scale there is no doubt in your mind what the tenths reading is.

There is no battery-operated lighting system.  None is needed.  The inside of the magnifier loupe is coated with a luminescent material that provides sufficient light to read the scales.

One of the shortfalls of most sextants has to do with telescope collimation.  You cannot simply slap a nonadjustable telescope into its mount without accepting some degree of accuracy loss.  The Keplerian telescope of the CHO-T can not only be adjusted for collimation, but it has parallel cross-hairs in the field of view to simplify this process. 

The sextant with the Keplerian telescope weighs just under 3.5 pounds.

All in all, when you look at the simplicity and common sense of all of these improvements, some of which could have been implemented  200 years ago, you really scratch your head and wonder why this was all left to the Soviets in the very dawn of sextant manufacturing and design.  So, now here's what I have done to bring this sextant up to factory release.

First, a word to the wise about buying one of these sextants, or a Freiberger for that matter, from the pawnbrokers who are simply selling them as is.  I have yet to buy a CHO-T that was not all but frozen from long hardened grease.  It often takes two to make one sweetheart (because of a defective, non-repairable major component) and a full refurbish effort requires a minimum of eight hours of work.  CHO-T sextants were largely military and merchant marine issue.  As such, they rarely found their way into the hands of owners who were willing to give them ongoing TLC.  If it doesn't indicate refurbished, it's something you'll have to figure out on your own.

That being said,  I have completely broken down and re-lubricated this sextant to the last bolt and spring.  I have squared the index mirror to the frame,  adjusted out side error of the horizon mirror and reduced the index error to less than a half minute of arc on either side of zero on a star-on-star sighting.

I have cleaned and lubricated both telescopes and collimated the Keplerian telescope.

I have also cleaned and lubricated the magnifier loupe and I have put a fresh thick coating of strontium-90 (just kidding - 88) aluminate paint on the loupe interior.

The mirrors are in near perfect condition as are the shade lenses, although the index mirror has some micro-scratches which you really have to look closely to see.  Also included is your choice of the standard spare index mirror (although back-silvered) or a spare first surface  index mirror which I manufacture myself. 

Overall, the sextant has some cosmetic un-niceties in that it has seen its share of time at sea.  However, it is mechanically flawless and the components seem all original.

The sextant comes with a 3G iPod loaded with Starpilot (a very powerful celestial navigation program) the nautical almanac to the year 2050 and several other apps which are useful in celestial.  The iPod has a screen protector. It comes with a charging wire.  The battery in the iPod is not new, but it seems to hold a charge for a significant amount of time.

In addition, I am including an ultraviolet flashlight for charging the magnifier loupe.  With a three-second blast from the UV light, the strontium aluminate paint is charged for about 15 minutes.

If you want to clear the lunar distance to make accurate sights to calculate GMT, this is your first choice of sextant above all others. The Freiberger is close in accuracy, and makes a good second choice for this purpose.

The books in the pictures are not included, but if you are a novice, I will part with a copy of Mariner's Celestial Navigation by Crawford for $15 extra.

Disregard the time limit eBay suggests for shipping.  These instruments need to be tweaked out of storage, which requires a series of good celestial sights.  So, depending on sky coverage, this could take up to a week.

I have sold many sextants on eBay, both marine and aviation, but I have been out of action for more than a year now. So, if you want to see my past reviews you will have to dig for them a bit by pasting this URL into your search bar: https://www.ebay.com/fdbk/feedback_profile/balloonron?user_context=BUYER and clicking on "Received as seller."

You can see my regular day job by searching customnine balloons.