Baldwin Calculating Engine

This is one of few surviving examples of a production model of the pinwheel calculating machine patented by Frank S. Baldwin of St. Louis in 1875. On a pinwheel calculating machine, digits are represented by retractable pins. Setting the machine consists of moving levers that release an appropriate number of pins, which are engaged when the crank rotates. Baldwin’s pinwheel mechanism was not widely adopted in the United States, although the pinwheel machine proposed slightly later by the Swede W. T. Odhner was most influential.
This non-printing machine has a brass base with two brass pieces on the side that serve as a frame. The brass has a dappled finish. A brass cylinder is mounted horizontally toward the back on a shaft that joins the pieces of the frame. The cylinder is 7 cm. (4-3/4”) in radius and 7 cm. in length. It has six round holes on each end. The cylinder may be moved along the shaft by releasing a catch on the left side and rotating the large crank on the left. Rotating this crank also drives the machine.
The surface of the cylinder has eight oval openings that reveal a set of number wheels, and two rows of four metal buttons. A brass screw is on the left end. By depressing a button and turning the screw, one changes the digit showing in one hole and the number of pins protruding from the other side of the cylinder.
In this way, one can enter up to eight-digit numbers. When the cylinder is turned, the pins act on a set of intermediate wheels that move both smaller, upper wheels toward the front to show a result as large as 17 digits, and lower wheels that indicate the multiplier, up to eight digits. Beneath each of these rows is a slide to indicate decimal divisions. A lever at the left front of the machine lifts a set of small rubber wheels, making it possible to zero the result wheels using a small crank on the right.
The machine has no maker’s mark.
Compare to the patent model, MA*252698.
Baldwin made ten of these machines, including the patent model. This example was owned by Joseph S. McCoy, actuary of the U. S. Treasury from 1889 until his death in 1931. McCoy and his predecessor, Ezekial Brown Elliott, were most open to inventions in adding machines.
Accession file.
F. S. Baldwin, "Improvement in Calculating-Machines," U.S. Patent 159244, February 2, 1875.
“Baldwin’s Arithmometer,” Philadelphia, Reliance Machine Works, about 1875. This brochure indicates that Baldwin’s calculating engine sold for between $150 and $250.
Katsunori Kadokura, “Wann baute ”Odhner” seine erste Maschine, 1874 oder 1876?,” #29, Historische Bürowelt, 1990, pp. 7–8.
P. A. Kidwell, “The Adding Machine Fraternity at St. Louis: Creating a Center of Invention, 1880–1920,” IEEE Annals of the History of Computing, 22 #2 (April-June 2000), pp. 4–21.
L. Leland Locke, “The History of Modern Calculating Machines, an American Contribution,” American Mathematical Monthly, 31 #9 (Nov 1924), pp. 422–429.
Accession file.
Currently not on view
date made
Baldwin, Frank S.
place made
United States: Missouri, St. Louis
Physical Description
brass (overall material)
rubber (overall material)
steel (overall material)
overall: 15 cm x 19 cm x 21.5 cm; 5 29/32 in x 7 15/32 in x 8 15/32 in
ID Number
catalog number
accession number
Credit Line
Gift of Mrs. Joseph S. McCoy
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Calculating Machines
Data Source
National Museum of American History, Kenneth E. Behring Center


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