In 1870 Nels Ockerlund (1837–1903), a Swedish immigrant (he immigrated to the United States in 1865 and settled in New York City, and became a citizen in 1879), patented two calculating devices—an improved rule and calculator (U.S. Patent 102034 issued 19 April 1870), and improved adding-machine (U.S. Patent 105717 issued 26 July 1870).

The patent model of the first device (up to 1880, the US Patent Office required inventors to submit a model with their patent application) is still preserved in the National Museum of American History, Washington, D.C. (see the nearby image).

Ockerlund’s Rule and Calculator is made of wood and German silver, and has overall measurements: 3.2 cm x 17.7 cm x 4.4 cm. This combined instrument may be used to measure distances of up to 24 inches, to measure angles, to solve problems relating to ratios, to assist in finding the area of triangles when the lengths of three sides are known, and to add three-digit numbers. It is in the general shape of a four-fold rule, with a wooden core covered on both sides with German silver. A scale of inches, divided to 1/16″ and numbered by ones from 1 to 12 twice, runs along the outer edges of the arms. Along the inner edges of both arms are scales of equal parts, with 30 parts to the inch.

A protractor is at the center joint. A hollow in one arm contains two rules. One rule unfolds to reveal a 10″ scale and a scale of 30 parts per inch. The other rule has a 4-1/2″ scale and a scale of 30 parts per inch. These rules are supposed to attach to slides that move in a groove in one of the arms, allowing the solution of problems of proportion. To add numbers, one removes the longer rule from the groove, and places it alongside the scale on the arm.

A third rule slides and pivots in a hollow in the other arm. Using this rule and the two arms of the instrument as sides, one can represent a triangle. The grooved arm serves as the base and a rule sliding in the groove measures the height of the triangle, from which one can calculate its area.

For the second calculating instrument of Ockerlund—the adding device, we have nothing but the patent application (see the nearby patent drawing). This simple calculating instrument is similar to the earlier device of John Nystrom (another Swedish immigrant in the USA) from 1851.

The invention has for its object to furnish a simple and convenient machine, by means of which numbers may be added and subtracted quickly and accurately, and which will enable the several amounts or differences to be registered as obtained. It has a plate, circular in general form, which has a wide circular groove formed in its face, in such a way as to leave a narrow rim around its outer edge, and a small circle at its center.