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Perrygraf Load Center Unit-Sub Slide Rule for Allis-Chalmers

National Museum of American History

Object Details

Perry Graf Corporation
Description
This rectangular gray and orange cardboard rule has a cardboard slide and is held together by six metal rivets. The front of the rule explains that the calculator helps users select and test the proper air circuit breakers for electrical substations constructed by Allis-Chalmers. The front of the slide provides reasons why breakers were essential in old and new substation systems. The back of the rule has four logarithmic scales for reading the key number (from the transformer rating), then the index number, then the circuit capacity, and then the amp load. The scales on the slide are color-coded so the user could easily see which level of interrupting capacity was needed.
According to a mark on the slide, Perrygraf Corporation made this instrument, which Allis-Chalmers copyrighted in 1943. While the company is perhaps better known for manufacturing farming equipment, it also built generators, turbines, compressors, and other machinery for heavy industry. Additionally, its engineers designed electrical substations. The company ceased manufacturing operations in 1998. For more on Perrygraf, see 1979.3074.03. For another slide rule made by Perrygraf for Allis-Chalmers, see 1983.3009.04.
Reference: Allis-Chalmers, "Three 'Not-so-Secret' Weapons," The Ohio State Engineer 28, no. 2 (December 1944): 16–17.
Location
Currently not on view
Credit Line
Transfer from Smithsonian Institution Libraries
1943
ID Number
1983.3009.06
catalog number
1983.3009.06
nonaccession number
1983.3009
Object Name
calculating rule
slide rule
Physical Description
metal (part material)
paper (overall material)
Measurements
overall: .2 cm x 23 cm x 9.6 cm; 3/32 in x 9 1/16 in x 3 25/32 in
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Slide Rules
National Museum of American History
Subject
Mathematics
Rule, Calculating
electricity
Engineering, Electrical
Record ID
nmah_694152
Metadata Usage (text)
CC0
GUID (Link to Original Record)
https://n2t.net/ark:/65665/ng49ca746a5-1026-704b-e053-15f76fa0b4fa

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Slide rule - Allis-Chalmers Load Center Unit-Sub Rule - Front View
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