Felsenthal FDD-7 Nautical Course Protractor Manufactured for DanforthWhite

This white plastic circular protractor is mounted on a clear plastic square plotting board with green grid lines. The board bears a white arc for correcting against compass errors of VARIATION, divided to single degrees and marked by tens from 30 to 0 to 30. The letters E and W are printed above the 25° points. The protractor is divided by single degrees and marked by tens from 0° to 350°. A compass rose, with an arrow at North and the letters E, S, and W inside triangles, appears inside the degree circle.
An extending arm is affixed to the center of the protractor. The end of the arm on the protractor is marked with +2 (in black), +4 (in green), and +1 (in black). The arm also bears an arc for correcting against compass errors of DEVIATION, divided by single degrees and marked by tens from 20 to 0 to 20. The letters E and W are printed above the 15° points.
The part of the arm that extends for 9-3/4" beyond the protractor is divided by tenths and labeled for NAUT[ICAL] MILES. Markings by ones from 1 to 5 are for a scale of 1:40,000 n.m.; markings by ones (in green) from 1 to 10 are for a scale of 1:80,000 n.m.; and markings by ones from 1 to 2 are for a scale of 1:20,000 n.m. The arm is marked with instructions for use: Set 0 on compass circle to variation on square base. Align arm with course. Align cross lines on base with any meridian or parallel on chart so arrow on base points north. Read compass course on compass circle opposite deviation on arm. Deviation may be marked inside compass circle.
A sheet of instructions is also provided with the instrument and its clear plastic sheath. The arm is marked with the object's name—DE LUXE COURSE PROTRACTOR (/) PAT. PENDING—the Danforth/White company logo—the letters DW with the slogan, THE MARK OF SAFETY AFLOAT—and the maker's mark: DANFORTH/WHITE (/) PORTLAND, MAINE (/) ©1959, by R. S. Danforth. Felsenthal Instruments Co. manufactured this protractor for Danforth/White, which made well-regarded nautical compasses in the 1960s. Since the 1980s, the company has sold weather stations and instruments under the name Maximum Inc. For Felsenthal, this protractor was product number FDD-7.
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, 1977.1141.21, 1977.1141.22, 1977.1141.23, 1977.1141.24, and 1977.1141.30.
Currently not on view
date attributed by donor
Physical Description
paper (overall material)
metal (overall material)
plastic (overall material)
overall: .2 cm x 34.5 cm x 10.3 cm; 3/32 in x 13 19/32 in x 4 1/16 in
ID Number
accession number
catalog number
Credit Line
Gift of Ben Wharton Rau and Margery Felsenthal Rau
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Data Source
National Museum of American History, Kenneth E. Behring Center


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