Ross Precision Computer Circular Slide Rule
date: label: date made
content: ca 1921
name: label: maker
content: Computer Manufacturing Company
notes: label: Description
content: This circular slide rule consists of a silver-colored metal dial, 8-1/2" wide, mounted on a silver-colored metal disc. Three oblong holes on the base disc permit the reading of trigonometric scales on a white celluloid and cardboard disc that is between the metal discs. The celluloid disc is marked: COPYRIGHTED (/) L. ROSS, SAN FRANCISCO (/) PATENTS PENDING.
label: Description
content: On the front of the instrument, the top dial is divided along the outer edge into 400 equal parts. In each quadrant of the dial, the scale is marked from 100 to 1,000, with every tenth division marked. Inside of this scale, there is a spiral scale with 25 coils divided logarithmically from 0 to 1,000, making the rule equivalent to a linear slide rule about 50 feet long. These scales are marked in purple and are worn away in several places, including around much of the edge and underneath where the indicators rest.
label: Description
content: Affixed to the center of the disc is a brown metal linear rule, 1-1/8" wide, marked with N, M (Sum), D (Difference), and Root scales. This rule is made of three pieces, but the center no longer slides. Also affixed to the center is a yellow celluloid hairline indicator, 3/4" wide, and a second yellow celluloid indicator, 1-1/2" wide. This indicator is marked on the left side by fours from 0 to 100, labeled Quadrants, and on the right side at varying intervals from 100 to 1,000, labeled Nos. It is attached to a metal handle lined with yellow-white celluloid. The handle is also attached to a pivot at the center back of the instrument. The handle is marked: THE ROSS (/) PRECISION COMPUTER (/) Computer Mfg. Co. (/) San Francisco. The handle has reminders for setting the device for multiplication, division, and proportion, and there is a thumbscrew for making adjustments.
label: Description
content: The instrument also came with a loose, wedge-shaped piece of yellow celluloid with a hole at one end for attaching to the center of the computer. It is marked with the names of various trigonometric functions and various angles. The round part of the instrument fits into a black leather case with two snaps, stamped both inside and outside: x THE ROSS ÷ (/) PRECISION COMPUTER (/) COMPUTER MFG. CO. (/) SAN FRANCISCO U.S.A. (/) PAT. PEND. COPYRIGHTED. An instruction manual (1996.3077.02) and a letter and advertising literature (1966.3077.03) sent to the purchaser, Roy Kegerreis of New York, were received with this instrument. The letter is dated July 31, 1918, and the manual was copyrighted in 1919.
label: Description
content: Louis Ross of San Francisco designed three circular slide rules in the 1910s: the Precision Computer, the Meridi-o-graph, and the Rapid Computer. Advertisements and reports of surviving instruments indicate that the Precision Computer varied in appearance and size.
label: Description
content: The Computer Manufacturing Company sold the Precision Computer for $20.00. A clamp for mounting the rule above a desk sold separately for $2.50. The company claimed its customers included the Panama Canal Commission, DuPont Powder Works, and General Electric. The company's offices were originally located on 25 California Street in San Francisco; in 1921, the factory moved from 268 Market to 340 Sansome. The Sansome address is handwritten inside the instruction manual, suggesting Kegerreis learned about the computer in 1918 but did not purchase one until 1921.
label: Description
content: Dr. Roy Kegerreis (1886–1968) obtained his BS in Electrical Engineering from The Ohio State University in 1907, his MS in Mathematics from Harvard, and his PhD in Physics from the University of Michigan in 1917. At the time he purchased this slide rule, he apparently was living in New York City. Kegerreis went on to get an MD in 1934, and he worked for many years as a radiologist. This slide rule was given to the Smithsonian by his daughter, in his memory.
label: Description
content: References: Accession file; Edwin J. Chamberlain, "Long-Scale Slide Rules," <i>Journal of the Oughtred Society</i> 8, no. 1 (1999): 24–34, "Long-Scale Slide Rules Revisited," 13, no. 1 (2004): 23–43, and "Circular Slide Rules with Very Long Scales," 17, no. 1 (2008): 52; "A Five-Place Calculating Device," <i>Electrical World</i> 66, no. 11 (1915): 604; "San Francisco Companies Move to New Quarters," <i>San Francisco Business</i> 3, no. 19 (November 11, 1921): 22; "Ross Precision Computer," NIST Museum Digital Archives, http://nistdigitalarchives.contentdm.oclc.org/cdm/ref/collection/p15421coll3/id/266.
label: Location
content: Currently not on view
place: label: place made
content: United States: California, San Francisco
topic: label: Subject
content: Rule, Calculating
label: Subject
content: Invention
label: Subject
content: Engineering
label: Subject
content: Mathematics
label: Subject
content: Business
setName: label: See more items in
content: Medicine and Science: Mathematics
label: See more items in
content: Science & Mathematics
label: See more items in
content: Slide Rules
creditLine: label: Credit Line
content: Gift of B.K. Lunde, in memory of Roy Kegerreis
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: 1996.3077.01
label: nonaccession number
content: 1996.3077
label: catalog number
content: 1996.3077.01
objectType: label: Object Name
content: calculating rule
label: Object Name
content: slide rule
physicalDescription: label: Physical Description
content: metal (overall material)
label: Physical Description
content: leather (case material)
label: Physical Description
content: plastic (cursor material)
label: Measurements
content: overall: 31 cm x 25 cm x 2.7 cm; 12 7/32 in x 9 27/32 in x 1 1/16 in