Kegelman Stadia Reduction Computer Circular Slide Rule

This white plastic circular rule has a clear plastic indicator attached with a metal grommet in the center. The rule has scales of H (horizontal factor), theta (vertical angle), and V (vertical factor). A diagram on the instrument gives the formulas for these factors. The instrument is marked: KB (/) STADIA REDUCTION COMPUTER (/) KEGELMAN BROS. (/) HUNTINGDON VALLEY PA. (/) COPYRIGHT, 1956 (/) BY WILLIAM KEGELMAN P.E. It is in a cream-colored paper envelope stamped: WILLIAM KEGELMAN (/) 393 COUNTY LINE ROAD (/) HUNTINGDON VALLEY, PA.
George Kegelman (1900–1985) began his career with Heller & Brightly of Philadelphia. He established his own shop around 1943 and began to work with his brother, William (1907–1985). In 1951, the pair formed Kegelman Brothers, which became best known for its Model 101 engineers transit. William Kegelman received a copyright (A245443) for this device, which was intended to process readings taken with the transit, on July 9, 1956.
For other slide rules for reducing data from observations made with stadia rods, see MA*333636, 1977.1141.41, 1983.0472.01, 1987.0221.01, and 1987.0221.02.
References: Robert C. Miller, "George Kegelman and Kegelman Brothers: Mathematical and Optical Instrument Makers," Rittenhouse 5 (1991): 56–58; Charles E. Smart, The Makers of Surveying Instruments in America Since 1700 (Troy, N.Y.: Regal Art Press, 1962–1967); Catalog of Copyright Entries: Books and Pamphlets, 3rd ser. 10 (1956): 324, 1161; Kegelman Bros., Instruction Manual for Engineers Transit (Hunting[d]on Valley, Pa., 1957) 9–10 (see 2001.0282.02).
Currently not on view
Object Name
calculating rule
slide rule
date made
after 1956
Kegelman Bros.
Physical Description
plastic (overall material)
metal (part material)
paper (part material)
rule: 12.9 cm; x 5 1/16 in
overall: 13.2 cm x 13.2 cm x 13.2 cm; 5 3/16 in x 5 3/16 in x 5 3/16 in
envelope: 13.3 cm x 13.3 cm; 5 1/4 in x 5 1/4 in
place made
United States: Pennsylvania, Lower Moreland Township
ID Number
accession number
catalog number
Rule, Calculating
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Slide Rules
Data Source
National Museum of American History, Kenneth E. Behring Center


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