Felsenthal Range Deflection Protractor

Description
This clear plastic sixth-circle protractor is graduated into 10 groups of 20 divisions, each labeled with the number 50. The unit of angular measure is mils, which was utilized in artillery applications. There are 6,400 mils in a circle (i.e., 1 mil = 0.05625 degrees). The arc on this instrument is 1,000 mils, or 56.25 degrees, in length.
An arm extends from the left side of the protractor. The arm is divided to half-units and marked by five (scaled) meters from 160 to 10. Two holes with diameters of 5mm are next to the 145–140 and 30–25 marks. The vertex of the protractor bears a small notch.
The interior of the protractor is marked: PROTRACTOR, RANGE DEFLECTION (/) SCALE 1:25,000 (/) RANGE 16,000 (/) METERS. Stamped inside a box is the text: THIS TRAINING AID WILL BE RETURNED (/) TO THE FIELD ARTILLERY SCHOOL (/) UPON COMPLETION OF THE SUB-COURSE (/) WITH WHICH ISSUED. Donor Ben Rau dated the instrument to 1965.
See also 1977.1141.01, 1977.1141.02, 1977.1141.05, 1977.1141.08, 1977.1141.09, 1977.1141.10, 1977.1141.11, 1977.1141.12, 1977.1141.18, 1977.1141.19, 1977.1141.20, 1977.1141.21, 1977.1141.22, 1977.1141.23, 1977.1141.24, 1977.1141.30, and 1977.1141.39.
Location
Currently not on view
Object Name
protractor
date made
1965
maker
Felsenthal Instrument Co.
Physical Description
plastic (overall material)
Measurements
overall: .2 cm x 41 cm x 66.5 cm; 3/32 in x 16 5/32 in x 26 3/16 in
ID Number
1977.1141.03
accession number
1977.1141
catalog number
336387
subject
Mathematics
Protractor
Artillery
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Protractors
Data Source
National Museum of American History, Kenneth E. Behring Center

Comments

How is the protractor used?Thanks

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