Nels Ockerlund, Patent Model for Combination Rule, Protractor, and Calculating Device, 1870, Smithsonian Institution negative number DOR2013-16385.

The U.S. Patent Office collected about 200,000 models to accompany the 246,000 patent applications received by the office between 1790 and 1880 before it was decided that 3-D mock-ups would no longer be required from inventors. Thousands of models had burned in a fire at the Patent Office Building in 1877, but thousands remained to be stored and maintained. The U.S. Congress attempted to disburse the collection in 1908 and 1926, transferring over 16,000 of the patent models to the Smithsonian.

One of these objects was designed by Nels Ockerlund (1837–1903), an emigrant from Sweden who settled in New York City. Combination instruments were popular with draftsmen, builders, and engineers, so Ockerlund devised a tool that measured distances of up to 24 inches, measured angles, solved problems relating to ratios, assisted in finding the area of triangles when the lengths of three sides are known, and added three-digit numbers. The instrument folded up so that users could easily keep it in a pocket or in a case of drawing instruments.

This object and other rulers, scales, and length measures from the Smithsonian's National Museum of American History are now shown and described at the website http://americanhistory.si.edu/collections/object-groups/scale-rules.

Index of Mathematical Treasures

Index of Mathematical Objects