Introduction to ISRM and Slide Rules

Our Mission, Gifting Policy and Privacy Statements

ISRM is a 501(c)3 (A57 - Science and Technology Museums) Colorado non-profit corporation. Colorado ID Number 20181884948, IRS EIN 83-2486423, as International Slide Rule Museum dba ISRM - ISRM Advisory Board of Directors.


Donations are
tax deductable


What is a "Slide Rule"? A slide rule is a mechanical analog computer that was invented over 320 years ago and 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.

If you are wondering about the process of creating images for posting slide rules specimens, here is a 7 minute video captured from my screen while editing the many scans required to document a slide rule into one single image.ISRM Scanning Procedure Screen Capture

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.
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.

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


Calculators Before The CPU
PDF version
This article was written for the ASME Mechanical Engineering Magazine for their September, 2014 issue. ISRM 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 a 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 physical or virtual 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.


Note: Donations of slide rules are currently subject to approval, based on their usefulness to fill the gaps within the galleries, or have significant provenance of historical figures. Please contact the curator.

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 eadily accepted. However, damaged or very common slide rules may not be able to replace those in the galleries. 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. It may take a few months before your donation shows up in the galleries, so please be patient. We also accept collections from slide rule enthusiests, wishing to downsize their homes, in order to preserve their artifacts.

Potential and Past donors please review the following document:
ISRM Future of Accessioning, Deaccessioning, Transfer & Disposal (.PDF) Revised 05-04-2023

Please contact:

1944 Quail Circle
Louisville, CO 80027
United States

ISRM Deed of Gift Form (.pdf)
ISRM Deed of Gift Form (.doc)


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. 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!

Please make personal checks or Money Orders payable to: ISRM

To contribute
toward downloads:

Donations are
tax deductable


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


The International Slide Rule Museum began as a one-man's collection of slide rule as was shown on Michael Konshak's personal website. As the website grew in numbers, Michael envisioned a future of having a brick-and-mortar museum, either as a standalone entity or as part of an existing physical museum. The sliderulemuseum.com website was created in 2003 as a mechanism to began the process of fulfilling that goal. Part of having a complete collection relies on having artifacts of that would be interesting to visitors. Many owners expressed a desire to gift rare artifacts, but wanted the ability to deduct the Fair Market Value (FMV) of the donations on their I.R.S. taxes. In response to these requests, in 2018, ISRM became incorporated in the State of Colorado and were given an official non-profit status by the I.R.S. and has a Board of Advisors.

ISRM, LLC is still a one-man operation with Michael Konshak as the President and Curator.and the corporation has a board of directors with a Secretay and Friends of the Museum as a Board of Advisors.The future of ISRM is uncertain, as the hopes of the collection to be hosted and displayed in a brick-and-mortar museum has diminished. Most likely, the best we can hope for is to preserve the images of the specimens and maintain a virtual museum via the website, but with the intent of making the website more modern and mobile friendly. The physical artrifacts most likely will have to be transferred or sold on a piecemeal basis. This is necessary, in part because there is a need to relocate the ISRM offices to a part of the united States that is more conducive to the health of curator and his family. There is no plans as yet. Input is weclome.

* 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).

Copyright © 2003-
International Slide Rule Museum