Davis plastic sextants have emerged as truly viable instruments for celestial navigation. Their accuracy is not as great as with metal sextants, and their errors vary with temperature, making frequent IC checks advisable. They make acceptable “first” sextants if finances are a constraint, and are always useful as back-up sextants. The MK 25, and MK 15 (shown above) have the same basic construction. The former is gray in color, and is said to be of a more stable plastic which is resistant to temperature changes. The latter is black in color. The MK 15 has a traditional split mirror, and is non-illuminated. MK 25 has illumination and a whole horizon mirror. Both sextants come with an instruction booklet, plastic carrying case, neck lanyard, 3x scope. and a sight tube.