Felsenthal A-10 Protractor and Map Coordinator

This clear plastic semicircular protractor is divided by ten mils and marked by hundreds from 100 to 3,100 in both the clockwise and counterclockwise directions. It is also divided by single degrees and marked by tens from 0° to 180° in both directions. Diagonal lines extend some of the measurement markings out to the edges of the rectangle surrounding the protractor. Pinholes are at the origin point and in the upper left and right corners. The interior of the protractor has cutout stencils for a circle, triangle, square, and two oblong shapes. The middle also contains scales placed at right angles to each other. They are divided and marked by hundreds from 1,000 to 2[00]. The scales are labeled: 1:21120.
The left edge of the rectangular plastic piece is divided by tenths of an inch and marked by ones from 1 to 3. Inside the 3-inch ruler is a scale for mils divided by hundreds and marked by thousands from 5,000 to 1,000. The scale continues on the top of the rectangle, again divided by hundreds and marked by thousands from 5,000 to 1,000. The scale is labeled: 1:62500. On the right side of the top is a scale labeled: 1:20,000. It is divided and marked by hundreds from 1,000 to 2[00]. This scale also repeats on the right side of the rectangle. On the right edge of the rectangle, there is a scale divided by millimeters and marked by ones from 1 to 7. It is labeled: METRIC.
The bottom of the protractor bears a scale divided by hundreds and marked by thousands from 1,000 to 8,000. It is labeled: 1:62500. The bottom edge has a second scale, divided by hundreds and marked by five hundreds from 500 to 3,000. It is labeled: 1:21120. The name of the instrument is printed on the very bottom edge: MAP COORDINATOR AND PROTRACTOR - A-10. Donor Ben Rau dated the object to 1942.
See also 1977.1141.01, 1977.1141.02, 1977.1141.03, 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, 1977.1141.22, 1977.1141.23, 1977.1141.24, 1977.1141.30, and 1977.1141.39.
Currently not on view
Object Name
date attributed by donor
Physical Description
plastic (overall material)
overall: .1 cm x 13.9 cm x 8.7 cm; 1/32 in x 5 15/32 in x 3 7/16 in
Place Made
United States: Illinois, Chicago
ID Number
accession number
catalog number
Science & Mathematics
See more items in
Medicine and Science: Mathematics
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
Gift of Ben Wharton Rau and Margery Felsenthal Rau

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