Country of Origin: United States of America
3-D Test: 0.3 x 20.3cm (1/8 x 8 in.)
Cursor: clear plastic
This is a special purpose slide rule, which was used by pilots to determine true airspeed, based on indicated air speed, altitude, and other instrument readings. It is typical of the many specialized slide rules used for air navigation and flight management, before the advent of electronic calculators and satellite-based navigation systems.
The slide rule was found with a collection of paper archives that were donated to the Smithsonian in 1957.
Bequest of the Estate of E.L. Jones.