William A. Davis was an Englishman who settled in San Leandro, California,
and offered a range of inexpensive plastic nautical instruments for boating
enthusiasts. He introduced the Mark III sextant in 1963, and the instrument is
still in production. Like the sextant that Cruver made for the U.S. Maritime
Commission during the war, the Mark III is made of polystyrene. It has a simple
eye tube, and a scale that is graduated every degree from -35o to +100o and read by vernier to 2 minutes of arc. The original Mark III cost $9.95. This example was probably made in the late 1960s.
Ref: William A. Davis, How to Find Your Position with a Sextant (San Leandro, 1966 and 1968).