In January 1942 the Pioneer Instrument Division of Bendix Aviation received a
contract worth $1,068,000 to make 2400 A-7 aircraft sextants for the Army Air
Corps. The A-7 was based on the instrument that Pioneer had introduced in 1931, but equipped with a finger activated pencil that enabled the navigator to make a number of vertical marks on a piece of roughened gray paper mounted below the index knob. After each series of shots, these marks would be visually averaged, and the average time of the series determined from a stopwatch. Although the technique was relatively crude, the Army boasted that an experienced navigator using an in instrument of this sort could "set his plane down at the end of a transoceanic flight within an error radius of only 15 miles, less than four minutes’ flying time."
Ref: "Aerial Navigation. It Guides U. S. Planes on World’s Longest
Flights," Life 13 (28 September 1942).
Eclipse-Pioneer Division, Bendix Aviation Corporation, Pioneer Aircraft
Instruments (1943), pp. 72-73.
Emanuele Stieri, Aircraft Instruments (New York, 1943), pp. 152-157.