overall: .2 cm x 15.3 cm x 3.7 cm; 3/32 in x 6 1/32 in x 1 15/32 in
This two-sided six-inch boxwood rule has a scale of chords and architect's scales dividing the inch into 45, 40, 35, 30, 25, and 20 parts on one side. The other side has an inch scale divided to 1/10" and numbered by ones from 1 to 6; a scale divided to single units and numbered by tens from 10 to 50 (10 units is approximately 3 cm); and 5" plotting scales with diagonal scales at each end. One plotting scale is divided to 1/2" and numbered by ones from 10 to 1, and the other is divided to 1/4" and numbered by ones from 1 to 19. The left edge of the rule is scalloped. Compare to 1977.1101.0018.
Similar scales (with the scallop on the right edge) were sold for 10–15¢ by Dietzgen (model number 1690) from at least 1902 to 1912 and by Keuffel & Esser (model number 1616) from at least 1892 to 1913. Both companies stopped advertising the object before 1921. The Department of Entomology at the National Museum of Natural History used this rule to study its collections.
References: <i>Catalog of Eugene Dietzgen Co.</i>, 6th ed. (Chicago, 1902), 135; <i>Catalog of Eugene Dietzgen Co.</i>, 7th ed. (Chicago, 1904), 162; <i>Catalog of Eugene Dietzgen Co.</i>, 9th ed. (Chicago, 1910-1912), 207; <i>Catalogue of Keuffel & Esser Co.</i>, 23rd ed. (New York, 1892), 126; <i>Catalogue of Keuffel & Esser Co.</i>, 33rd ed. (New York, 1909), 189; <i>Catalogue of Keuffel & Esser Co.</i>, 34th ed. (New York, 1913), 184.