This model has many great features including 7 large sunshades, a 3 mm x 27 mm star scope, and easy reading micrometer drum vernier scale that reads to 2/10’s of a degree. The Mark 15 has a 7" (18 cm) frame radius graduated from 120 degrees to -5 degrees and comes with a traditional half-silvered mirror. Our plastic sextants are lightweight and corrosion proof. Comes with instruction booklet.