Slide RulesCircular Slide Rules
Slide rules that are round offer the length of a 10" rectangular slide rule in a pocket-sized (roughly 3.6") format, since the scales are on the circumference of circles. The scales are also continuous, so there is no need to make adjustments, such as folded and inverse scales, for results of calculations that go off the ends of the scales. Furthermore, these instruments are relatively easy to construct: the scales are printed on one or more disks, and the disks or a single disk and cursor are fastened together with a pin at the center. However, this simple construction is also not very durable, and so circular slide rules may get out of position and thus they lack accuracy, compared to linear slide rules with slides that move along carefully grooved channels.
This collection suggests the diverse appearances and functions of circular slide rules that were manufactured between the mid-19th and late 20th centuries. For example, before Mannheim-type linear slide rules became popular in the late 19th century, American inventors patented a variety of circular designs. Some circular slide rules were made to look like pocket watches, while others were intended to promote particular businesses—Whitehead & Hoag and Perrygraf were especially influential American manufacturers of promotional items. Inventors and makers such as Albert Sexton, Louis Ross, Claire Gilson, Norman Albree, and Ross Pickett wanted their circular slide rules to compete with linear instruments in the engineering and education markets. Other circular slide rules were designed specifically for surveying, such as stadia computers, or for navigation, such as Dalton instruments that may also be seen in the Smithsonian's exhibition, Time and Navigation. Even more specialized in purpose were slide rules for grading earthworks, determining the effects of nuclear bomb explosions, writing efficient computer programs, and betting on horse races.
"Slide Rules - Circular Slide Rules" showing 1 items.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- References: Accession file; Edwin J. Chamberlain, "Long-Scale Slide Rules," Journal of the Oughtred Society 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," Electrical World 66, no. 11 (1915): 604; "San Francisco Companies Move to New Quarters," San Francisco Business 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.
- Currently not on view
- date made
- ca 1921
- Computer Manufacturing Company
- ID Number
- nonaccession number
- catalog number
- Data Source
- National Museum of American History, Kenneth E. Behring Center