The Ultimate Guide To Buying A Sextant

A sextant is one of the most recognisable navigational instruments. Unfortunately, it has been largely superseded by GPS, so fewer and fewer people are buying them. This has made finding reliable information quite hard to come by.  To help you out, I have created this guide which will guide you through the process I used when selecting my favourite sextant.

My favourite sextant is the Mark 15 Sextant from Davis Instruments. The best thing about it is that it balances affordability and performance, giving you a functional instrument for a reasonable price. Check out the current price on Amazon by clicking here.

What to look for when buying a sextant

When buying a sextant you are just looking for one that will do everything you need. You will find most are purely ornamental. Some are great for beginners, and others are top of the range, designed for maximum accuracy.

For today, I will assume that you are looking to buy a real, working sextant. If you are just looking for an ornamental one, you can buy based purely on looks and price. As we want to buy a real instrument, we need to weight up a few more options.

What is your experience level?

You want a sextant that will suit your experience level. Most people will fall into the category of beginner, but wanting a sextant that will give good results as their skill level increases. That is where the Mark 15 is perfect. It is still a precision instrument, but it is not so expensive that you are afraid to experiment as you are learning.

Once you master the instrument, the Mark 15 will give you a position that is accurate enough in most situations.

As your skill level increases, you might want to consider an upgrade if you intend to navigate with a sextant on its own. If, however, you just plan to carry a sextant as a backup in case your GPS fails, the Mark 15 will be just right.

What material is the sextant made from?

Sextants are either metal or plastic. Metal body sextants have a stronger frame and generally give more accurate results. The disadvantage of metal body sextants is that they do cost significantly more than plastic ones.

Plastic sextants are more susceptible to warping, damage, and are generally a little less accurate than metal sextants. Their major strength is that they are much more affordable than metal body sextants.

The Davis Instruments Mark 15 Sextant has a plastic body, making it one of the most affordable instruments on the market. Considering my normal use, the plastic body is not actually an issue for me. It is mostly stored in its box in a house. It is not continuously exposed to sunlight, or extremes of temperature. I don’t need to spend more on a metal frame.

As for the flexibility of the plastic frame, I consider that an advantage. I like to learn with my sextant, so I am happy to check and correct errors every time I use it. I just don’t need the additional strength of the metal sextant. Once you learn to navigate with a plastic sextant, you can switch to a metal one at any time. If you learn on a metal one, you might struggle to switch to a plastic one.


Most mirrors on the sextant are the same, regardless of the sextant you choose. The main variation comes in the design of the horizon mirror. Some have a single pane, “full horizon mirror” which are often considered easier to use. Others have a distinct “split-horizon mirror”.

The Davis Instruments Mark 15 has a split-horizon mirror. I prefer to use this sort of mirror because the mirrored part gives a full reflection, making it easier to pick out dimmer objects in the sky.

Why I chose the Davis Instruments Mark 15 Sextant

I chose the Davis Instruments Mark 15 Sextant primarily because I wanted an accurate, affordable instrument to improve my celestial navigation. The price difference between plastic and metal frames was too significant to be worthwhile for my circumstances.

Other affordable sextants were all lacking in some respect. For example, the Mark 3 is cheaper than the Mark 15, but it doesn’t have a locking arm, and it is just too different from other sextants to be worth learning.

Alternative sextants

Davis Instruments Mark 25 Sextant

The Mark 25 is a slight upgrade compared to the Mark 15. Its horizon mirror is a full-horizon mirror rather than the semi-horizon mirror of the Mark 15. Other than that it has an integrated LED to help you read the angle in low light conditions. If you prefer the mirror style of the Mark 25, it would be worth considering that, otherwise the Mark 15 will meet your needs in a more affordable way.