Rolling Navigation Ruler, 19th century

This brass rolling ruler is engraved with measurements on all four sides. There are rollers on either side of the ruler, connected by an axle. The object is well worn with a dent on one corner, and it is screwed together. There are inches on one side of the ruler, on the remaining three sides the hash marks are slanted in ascending and descending increments of ten towards the center of the ruler ending in 90 making degree angles. The names “Cary London” and “R.F. Crawford R.N.” are stamped on the tool. William Cary was an instrument maker in London in the late 19th and early 20th centuries. “R.F. Crawford” was the owner of the instrument; the “R.N.” represents Royal Navy.
This navigational instrument was used to plot courses on nautical charts and could be rolled across a chart without changing its orientation. The different sides were used for angle or scale corrections on the meridians or curved lines on a globe connecting the poles.
Currently not on view
Object Name
parallel rule
rolling ruler
overall: 15 1/2 in x 2 1/2 in; 39.37 cm x 6.35 cm
ID Number
catalog number
accession number
Measuring & Mapping
Maritime Objects
See more items in
Work and Industry: Maritime
Maritime Objects
Data Source
National Museum of American History, Kenneth E. Behring Center

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