Introduction to ISRM and Slide Rules

Our Mission, Gifting Policy and Privacy Statements



What is a "Slide Rule"? A slide rule is a mechanical analog computer that was invented over 320 years agoand uses logarithmic scales to multiply, divide and calculate exponents and many other math functions, not including addition and subtraction. It is not a ruler used for linear measurements.

ISRM is the world's largest free digital repository of all things concerning slide rules and other math artifacts. There are over 7000 Images or PDF's in the ISRM Galleries and Libraries.

ISRM is dedicated to the Students, Educators, Scientists and Engineers of the Past and Those Still Present, and to promote the lost art of Numeracy by providing resources and slide rules for education and other historic institutions. We accept donations of slide rules for inclusion in the galleries. ISRM is a member of the American Association of Museums and the Association of Northern Front Range Museums. ISRM was founded in 2003.

Our apologies, the site is not yet mobile-friendly. Currently there is not enough financial or human resources to update the site to modern smart phones and tablets.

Michael Konshak, the curator and self-described "Hairy-Eared Engineer *", inspects a 2011 new arrival. What is it?

After 4 years of research, a 1939 Laboratory Specialties catalog revealed one just like it, possible made by Acu-Rule Mfg. Co.

50 years of working (1960-2010), Here's all the
math instruments the curator used in his career


Calculators Before The CPU
PDF version
I wrote this article for the ASME Mechanical Engineering Magazine for their September, 2014 issue. I made the claim that the introduction of the Texas Instruments TI-30 scientific electronic slide rule caused the death of the slide rule, and received some flack from readers who insisted that the Hewlett-Packard HP35, released in 1972 at $395, was the first scientific calculator that killed the slide rule industry. they missed my very poorely explained point. Like the first automobiles that were produced, which were very expensive, the HP35 was like the "Winton" which was too expensive for the average worker (or student). It wasn't until Henry Ford used mass production and interchangeability of parts to bring the Ford Model T from a starting price of $700 down to $200, when he sold a million of them, did the horse and buggy begin to dissappear. The other car makers still tried to keep their prices high, like HP, and a very small percentage of the populace could afford their autos. The TI-30, with its single LSI chip, came out in June 13, 1976 for $25.00, and, for the first time, the electronic scientific slide rule cost less than the equivalent analog slide rule calculators made by K&E. It was after that that the families who owned the slide rule companies stopped manufacturing them. TI must have learned from Henry Ford, who wanted to serve the people, rather than the board of directors.


ISRM is the world's largest free digital repository of all things concerning slide rules and other math artifacts. There are over 7000 Images or PDF's in the ISRM Galleries and Libraries. The picture of Becky holding a 1903 4 foot Ding & Frage Excise rule in front of quad monitors, shows the ISRM archiving operation, and the 17" x 11-1/2" (A3) scanner that is used. There are scans or pictures of actual slide rules and related math arifacts in the museum or provided by collectors from around the world Every specimen is different in some way. There are over 4000 unique items at present dating from 1850. Duplicate model numbers in this collection have different cursors, scales, logos or construction features. Unlike most collectors who want pristine specimens, the museum enjoys getting slide rules that are marked with the original engineer's name especially when we are told what work they were used for, even if it only helped the owner get through college.

  • The prefix codes 'S0XX', 'P0XX', 'L0XX', 'MXX', etc were the original identification filing system and are not part of manufacturer's model numbers. Slide rules with this notation are no longer part of the active ISRM collection as they were gifted to the Computer History Museum. We would appreciate gifts of slide rules to replace these specific items.
  • The 'ISRM' prefix code means the specimen is part of the physical current collection available for public displays. All new acquisitions or donations are given this code along with an accession number of the form YY.MM.DD.XX.
  • The 'HSRC' prefix codes are slide rule images from Herman's Slide Rule Catalogue which are duplicated in the HSRC gallery.
  • The 'REF' prefix code denotes that this is a donated scan from an ISRM friend or other source that has been archived on this site..
  • When you click on the pictures you will get a 150 dpi FULL SIZE SCAN (note manuals are scanned at 200 dpi) of the slide rule.
  • Scales are listed as to the location on the slide rule. The FRONT side is arbitrarily determined by the presence ofthe most common scales A [B, C] D.

Scales are described using the above convention

This is a work-in-progress. The museum is being expanded constantly to add reference pictures of slide rules and ephemera provided from other collections and international sources as well as from new acquisitions acquired through donations. Some scans are being supplied by other collectors who use the site as a reference, credits are duly noted, when known. Electronic 'Slide Rule' Calculators and Abaci are the newest galleries being documented at ISRM.

Most of the scans are larger than can be fully displayed in a default browser. Microsoft Internet Explorer 6 uses Automatic Image Resizing to make it fit without scroll bars. To display an image at full size in order to see more detail, change your settings by navigating to: Tools/Internet Options/Advanced/Enable Automating Image resizing [uncheck box].


This collection of mathematical artifacts has taken quite a while and expense to accumulate and catalog. Consequently, my goal as the curator, was to not only provide research information at no charge to the public but also assist worthwhile educational and historical institutions in expanding their collections. So far, recipients have been the University of Colorado, the Math History Museum of the Smithsonian Institute, and the Computer History Museum. I also have instituted a Slide Rule Loaner program for educators which sends matching sets of 25 slide rules to schools for temporary (as long as a school year) use. The slide rules are provided through the generous abundance of collectors worldwide.
As of May 26, 2006, the majority of the physical specimens and files used to create this museum are now located at the Computer History Museum in Mountain View, California for preservation and display. Take time to visit CHM when you are in the area.


If you wish to give your slide rule or your parents or relative's slide rule a bit of immortality and especially to honor the work that was done in life, donations of slide rules (and related calculators) are readily accepted and will be well cared for and preserved for posterity. Please include a brief bio/profile of the owner for the display. A small portrait may be included. Along with being displayed in the ISRM galleries, every attempt will be made to install gifted specimens into a permanant display and in some cases re-gifted to another institution that may be looking for similar articles. Donors are given credit with the artifact and are also listed in the 'Friends of the Museum' page. See the Example below on how it may be presented. It may take a few months before your donation shows up in the galleries, so please be patient.

Please contact:

1944 Quail Circle
Louisville, CO 80027
United States


All the high resolution images of slide rules in the galleries and the PDF files of scanned books, manuals and instructions have been free to download since 2003. The policy of ISRM is to continue this practice, without restrictions in order to provide research and educational information to the world at large. However, running a web site of this size with a large amount of data does take a lot of time and effort and does incurr costs in hosting in order to provide the bandwidth. We get over 30,000 hits per day. If you have enjoyed the many offerings of ISRM, and would like to contribute toward its expansion, you can send money using the Secure Paypal button on the right. All monetary contributions will be used to pay for the web site service, support shipping for the Slide Rule Loaner Program or obtain additional items for public displays. Thank you for your support and consideration!

To contribute
toward downloads:


ISRM does not collect any information concerning any of its visitors. In the case of Paypal transactions, only Paypal has access to your information.

Display Example of a Slide Rule Donation:

S535 K&E 4092-3
K&E 4092-3 S/N 187247
Made in U.S.A. - All Glass cursor - Used 1926-1930
Front Scale
LL0, A [ B, S, T, C ] LL3, LL2, LL1
Back Scale
K, DF [ CF, CIF, CI, C ] D, L
Parker D. Shepperd (c1910-1963) used this slide rule at the University of Colorado in Boulder. Graduated 1930 with a mechanical engineering degree. Case has student's address at 1221 University, Boulder, CO, a fraternity house near the campus. Mr Shepperd worked in various firms designing commercial HVAC systems, such as General Electric in Schenectady, NY, and Johnson Service Company in Detroit, Cleveland, and Boston. One of his big projects was the John Hancock Building in Boston. Slide rule donated by his daughter, Marnie, and has now been permanently transferred, with other items, to the University of Colorado Heritage Center.

Leslie (My Dad) Konshak's Slide Rule
This was my father's, Leslie (Les) Konshak (1914-2010), slide rule. Like most things he had it was not elegant, always practical, and in this case is one of the least expensive out there. Yes, it's a Sterling 584 which many collectors wouldn't even give a second glance. Sometime along the way the slide rule broke and rather than toss it away, Dad (or Mom) epoxied it back together and was given a new life. Eat it up, wear it out, do with or do without.Dad passed on in 2010 at age 93. Mom passed on in 2003 at 84. They are both buried at Fort Logan National Cemetary in Colorado.

* Hairy-Eared Engineer - definition:
1) An engineer who's old enough to have hair growing out of undesirable places.
2) Who's been practicing engineering so long that he or she has already made all possible mistakes at least once.
3) A desirable person to have on a project to ensure the mission succeeds.
4) Quote: "Every project needs at least one hairy-eared engineer" Marvin B. Davis -1980.
(Marvin was one then and 34 years later, my barber can attest that I've finally made the grade).

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