Stanley London Mark 3 Sextant with Scope and Case The Mark 3 Sextant uses a lightweight, corrosion-resistant aluminum alloy, just as Freiberger, Tamaya, and C. Plath do in their lightweight sextants. This aluminum-alloy instrument at only 2 pounds, 8 ounces (1.13 kg) is easier to use than the traditional 4-pound brass models. The sextant is 9 3/8 inches (23.8 cm) wide, 9 inches (22.9 cm) tall, 5 1/4 inches (13.3 cm) deep. The sextant case measures13 inches (33 cm) wide, 10 1/2 inches (26.7 cm) deep, 6 1/4 inches (15.9 cm) tall. The Stanley London Mark 3 Sextant includes high quality sextant oil, an adjusting wrench, a brush, lens cloth, and a Quality Certificate specifying the sextant's +/-20 arcsecond accuracy throughout the arc.