The Stanley London Mark 3 Sextant represents the best quality marine sextant on the market for the price. This is not a reproduction, but an accurate and calibrated fully functional nautical sextant for marine navigation. There is a very minor sacrifice in potential accuracy (+/- 20 arcseconds throughout the arc, compared with +/- 10 to 12 arcseconds), which is inconsequential compared to the human error when taking sights from a moving small vessel. This Mark 3 is actually used by many professional navigators. The Mark 3 sextant has revolutionized celestial navigation: Never before has such a high-quality, accurate metal sextant been available at such a low price. The sextant's full 50 mm mirrors and shade glass are precisely machined and extensively tested for flatness using the Fresnel diffraction pattern method. The Mark 3 sextant's LED lighting of the arc and drum allows for convenient night sights. Two standard AA batteries fit in the sextant's handle (batteries not included), and a convenient thumb switch controls the lighting. The 3.5 x 40 scope has fully coated optics and a large 40 mm objective lens to yield a sharp 3.5-power non-inverted (upright) image. The sextant comes with a beautiful, high quality hinged hardwood case to store and protect the instrument. This sextant has a unique serial number and is fully functional and factory calibrated for navigation.