overall: .2 cm x 15.3 cm x 15.2 cm; 3/32 in x 6 1/32 in x 5 31/32 in
Mathematical instruments have long been used to assist in aiming weapons. This circular slide rule is one such device. Made for use in antisubmarine warfare, it has two scales on the base, two scales on a concentric disc atop this, and a rotating pointer pivoted at the center. The lower disc has scales for the speed in knots and the range in yard. The upper disc has scales for the bearing rate and angle.
A mark on the disc reads: BEARING (/) RATE COMPUTER (/) FSN 1A 1220-691-0962 (/) MK 138 MOD. 1. A mark lower on the disc reads: FELSENTHAL INSTRUMENTS CO. (/) MFR’S PART No. FNR-5A (/) MFR’S CODE 22040.
Felsenthal made bearing rate computers for the U.S. Navy from at least the 1950s until at least the year 2000. A tag received with the object indicates that this model was produced from 1965.
Compare 1977.1141.33, 1977.1141.34, 1977.1141.35, and 1977.1141.36.
U.S. Navy, <I>Operations Specialist Volume I, NAVEDTRA 14308</I>, 2000, pp 10-22 through 10-28. This volume was accessed online August 3, 2017.