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 plastic circular slide rule has a white base, with three concentric logarithmic scales, all numbered from 1 to 50. The outer scale is labeled “SHOW (3rd)”; each unit has six subdivisions. The middle scale is labeled “PLACE (2nd)”; each unit has three subdivisions. The innermost scale is labeled “RACES WON”; units are not subdivided. There is a clear plastic hairline indicator.
- A smaller gold disc lies atop the white one. It is pivoted at the center and has a logarithmic scale, running from 1 to 95 and marked: TOTAL RACES ENTERED. Two more logarithmic scales are visible through a window in the gold disc. These provide the total purses of the races the animal had entered and, finally, the performance-class factor rating. According to the donor, if F=number of first place finishes of a horse, S=number of seconds, T = number of thirds, R = number of races entered, and M= the total money won, the scale calculates the number [[100F + 33.333S + 16.666T]/R] + 1.12 M.
- The gold disc is marked: K2 (/) PERFORMANCE/CLASS CALCULATOR (/) COPYRIGHT 1972 K2 PUBLISHING CORP. Accompanying the calculator are a paper instruction booklet, a sheet of paper giving the formula calculated by the machine, and a computer printout showing a similar calculation. The 20-page booklet was also copyrighted in 1972 and indicates the method can be used for thoroughbred, harness, and greyhound racing. K2 Publishing Corporation was located at 475 Northern Blvd., Great Neck, N.Y., where an office building was built in 1967.
- Everything is stored in a black plastic case with a clear plastic front. Another slide rule for handicapping horse races is 1998.3050.02.
- Reference: Tom Wyman, "More About Slide Chart Devices," Journal of the Oughtred Society 16, no. 2 (2007): 15–18.
- Currently not on view
- date made
- K2 Publishing Corp.
- ID Number
- nonaccession number
- catalog number
- Data Source
- National Museum of American History, Kenneth E. Behring Center