Frederick Post Co., Demonstration Slide Rule, Versalog Model 1460 (77 in., Wood).
Credit: S. E. Watkins

Dr. Steve E. Watkins, Gamma Theta Chapter, Guest Editor for the Slide Rule Special Issue

Slide rules are mechanical computing tools that resulted from the application of mathematical principles to practical needs in science and industry.  These elegant devices were invented 400 years ago and contributed to the work of generations of scientists, engineers, technicians, and tradesmen.  These tools fell out of usage upon the introduction of the electronic calculator in the 1970s.  The special issue on “Advancement of Technology using Slide Rules,” IEEE-HKN The Bridge Magazine, Volume 121(1), 2025 (hkn.ieee.org) [Link to Issue] looks back at the application and technology of slide rules. The main articles in the issue are:

Partners in this historical overview are the Oughtred Society and the International Slide Rule Museum (ISRM). These organizations are dedicated to preserving information on slide rules in all of their variations and applications.

This web content gives supplemental material for the feature articles.  Our IEEE colleagues share their memories of using slide rules and images of slide rules from their collections.

EXAMPLE CALCULATIONS WITH A SLIDE RULE

Slide rules are designed to perform mathematical operations by positioning sliding scales.  An adjustable cursor provides additional flexibility.  The scales may relate to general calculations such as multiplication, division, and trigonometric functions or to specialized formulas such as aircraft ground speed and LC-circuit resonant frequency.

Figure 1a gives an example operation for the value of √2 using a Post Versalog slide rule.  The red-line cursor is aligned with”2” on the D fundamental scale; the value of √2 = 1.41 is shown on the R1 scale.

Figure 1b demonstrates the operation 1.4 x 3. The beginning (“1”) of the C fundamental scale is aligned with “1.4” on the D fundamental scale.  The cursor is aligned with “3” on the C scale and the D scale reads 1.4 x 3 = 4.2.  The latter operation uses the logarithmic scales for C and D to implement log(1.4 x 3) = log(1.4) + log(3) = Log(4.2).

(1a)

(1b)

Figure 1a. Cursor aligned for a square root (√2 = 1.41) using the D and R scales.
Figure 1b. Cursor aligned for a multiplication (1.4 x 3 = 4.2) using the D and C scales. Credit: S. E. Watkins

COVER FOR SPECIAL ISSUE "ADVANCEMENT OF TECHNOLOGY USING SLIDE RULES"

The cover image for the Special Issue “Advancement of Technology using Slide Rules” shows selected slide rules from the collection of the guest editor and the collection at Missouri University of Science and Technology.  The slide rules and other items are identified below.

  1. Pickett & Eckel Inc., Pickett Power Log Exponential (Log Log Dual Base) Slide Rule Model N 3-T.
  2. Gilson Slide Rule Co., Midget Circular Slide Rule.
  3. Pickett & Eckel Inc., Pickett Power Log Exponential (Log Log Dual-Base) Slide Rule Eye-Saver Yellow Model N3-ES
  4. Keuffel & Esser Co., Log Log Duplex Linear (Log Log Decitrig) Slide Rule Model 4081-3.
  5. Frederick Post Co., Duplex (Versatrig) Slide Rule Model 1450L with Post Veralog Slide Rule Instruction Text.
  6. Pickett & Eckel Inc., Pickett Trig Slide Rule Eye-Saver Yellow Model N 200-ES.
  7. Concise Co., Japan, Concise Circular Slide Rule No. 260.
  8. Eugene Dietzgen Co., Phillips Slide Rule and Dietzgen Self Teaching Manual.
  9. Kane Aero Co., Dead Reckoning Computer Model MK-6B.
  10. Frederick Post Co., Demonstration Slide Rule Versalog Model 1460

SLIDE RULES FOR ENGINEERS: CONTRIBUTIONS FROM IEEE MEMBERS

Slide rules were a ubiquitous tool for engineers before they were replaced with electronic calculators.  Many members across IEEE have strong memories of using these devices and many have kept their personal slide rule or “slipstick.”  Here are some contributed images and associated comments.

Alex Schneider, Beta Tau Chapter (Northwestern University), IEEE Life Fellow

At Northwestern I dated a young woman who was a math major. One day after class she went shopping for a purse at Marshall Fields, then the top department store in town. The sales lady showed her one after another, which she rejected as not big enough for her 11″ slide rule!

[Left] Pickett Model N600-ES, Sun Hemmi (Japan) Pocket Rietz Slide Rule Model No. 74, and Keuffel & Esser Co., Polyphase Linear Mannheim Model 4098. Credit: S. E. Watkins

  • Robert L. Baber, Professor Emeritus at McMaster University,  [Beta Theta Chapter (Massachusetts Institute of Technology), IEEE Life Senior Member] with circular slide rules he had while a student at the Massachusetts Institute of Technology beginning in 1954.

  • Robert M. McClure, [Psi Chapter (University of Texas-Austin), IEEE Life Member, top left] receiving an award for coming in first place in a slide rule contest as a freshman electrical engineering major at Texas A&M University in 1952.

  • Walter Banzhaf [Beta Nu Chapter (Rensselaer Polytechnic Institute), IEEE Life Senior Member] with a 7 ft slide rule used for teaching. You can read his article on slide rules here.

Howard Wolfman, Epsilon Iota Chapter (San Jose State)

My post versalog slide rule that got me through four grueling years at the University of Illinois Electrical Engineering program.

Rajeev Bansal, Beta Omega Chapter (University of Connecticut),  IEEE Life Senior Member

To the right is a photo of the ARISTO slide rule and its carrying case that I used during my undergraduate electrical engineering program (1971-1976) at IIT, Kanpur in India. It still has pride of place on the wall in my study!

Krishnamurthy Raghunandan, Eta chapter, IEEE Life Senior Member

Slide rule – the icon of engineering throughout the 1960 and up to late 1980s was one powerful tool for engineers. In particular, I appreciated the German brand, “Staedtler Electra”, which could solve complex number problems so essential to electrical engineers. Since calculators based on Intel’s processors and the handheld calculators from Texas Instruments did not start until the early 1980s, the slide rule was the king – all engineers had one usually in a nice case or carefully stored in their bags.

Do the earlier generation of engineers miss the slide rule? You bet, it was not just a tool, but a thing of pride. As science and engineering progressed, calculators have taken the slide rule’s place and are doing well, adding more functions and graphics along the way.

  • The Xi chapter of IEEE-HKN officers, with Department Chair R. Mark Nelms, display slide rules that were used by former members to teach their classmates how to use these devices in their classes prior to the introduction of the electronic calculator.

  • My Pickett slide rule took me through my freshman and sophomore years in Electrical Engineering at Georgia Tech. However, I was happy to replace it with a new Texas Instruments SR-50 calculator when I began my junior year.

    – Chuck Till, Beta Mu Chapter (Georgia Institute of Technology), IEEE Life Member

  • The photo shows my slide rule on the title page of the book “Delights of the Slide Rule,” which was one of my favorite books when I was in high school. From this book, I learned several ways to perform division using the slide rule.

    – Michael C. Loui, Alpha Chapter (University of Illinois-Urbana), IEEE Life Fellow

John D. McDonald, P.E., IEEE Life Fellow

During my five years at Purdue University from 1969 to 1974 to get my BSEE and MSEE degrees, I used a slide rule – there were no calculators yet from HP and TI. In power engineering we do a lot of rectangular to polar and polar to rectangular conversions. These take a lot of time on a slide rule. On a calculator there are buttons for R->P and P->R to make these calculations almost instantaneous. To save time, especially in graduate, I used a circular slide rule to get these calculations done much faster. I have a circular slide rule at home!

[Right] Dietzgen Self Teaching Manual coauthored by Ovid W. Eshbach, 1951-52 HKN President. Credit S. E. Watkins

[Left] K & E Slide Rule. [Right] Aristo Slide Rule.

Asad Madni, Iota Gamma Chapter (University of California-Los Angeles), HKN Eminent Member

Asad Madni- “My first class at RCA Institutes was DC Circuit Analysis with Professor Salvatore Adelphio. He told us we were going to have a quiz.  I had never heard of a quiz before.  They had always been called a test or exam so I thought it was some kind of a learning interaction. When I got to class the teacher handed out the quiz and I realized he meant exam. So, I started taking it and the teacher said “Mr. Madni, I know you speak English extremely well, but you seem to have difficulty understanding my instructions. I did not say this was an open-book exam.'” (I had been using his trigonometric and log tables book to compute the complex math problems.)  I responded with the statement, “Professor this is not a textbook”’ to which he turned and addressed the then all male class, “Gentlemen, does this look like a book to you?” As the class answered “yes,” I went on to explain that I was using the tables in the book to answer the math problems because I did not own a slide rule. The professor said, “You mean to tell me you’re going to complete this quiz using trigonometric and log tables?’ I answered that I was, and needless to say, I finished the exam before the rest of the students with an A grade. That day, Professor Adelphio loaned me a slide rule and instructed him to take it home and learn how to use it. I did, and I promised Professor. Adelphio that in one month, once I had saved up enough money, I would purchase my own slide rule to use on future quizzes instead of the tables.”

Henry L. Durrwachter, Epsilon Mu Chapter (University of Texas at Arlington), IEEE Life Member

The slide rule that I used throughout my undergraduate years (1967-1972) was a Dietzgen, which was presented to me during my senior year of high school (1967) by the Professional Engineers Club of Dallas.  I never actually used my slide rule during my 41 year career.  Instead, after it remained in my desk unused for a couple of years, I had it mounted into a shadow box (see attached photo) and it hung on my office wall for the remainder of my working career.  Interestingly, I had young engineers come into my office later in my career and ask what was in the shadow box.  I had to explain to them what the slide rule was and what it could do!  Today, I get those same questions from my grandchildren who come into my home office and see the slide rule on the wall.

Collins Radio circular slide rule: [Left] Front for calculations [Right] Back for constants

Frederick H. “Fritz” Raab, Green Mountain Radio Research LLC

[Left] Pickett Demonstration Model

[Right] Working Slide Rule Tie Clip

Hulya Kirkici, IEEE Fellow, Professor at the University of Southern Alabama

Gary Lynch, Iota Chapter (University of Missouri), IEEE Life Member 

Although I am a retired life member, and earned my BSEE in 1976, I used a slide rule only for the first 3 years of undergrad school. Electronic calculators were making their way into engineering while I was still in high school. My dad had one of the original HP-35 slide rule calculators (MSRP: $395, making it too valuable to trust to a teenager.) By the time I was a junior, enough of my contemporaries had slide rule calculators, and finished the tests so far ahead of the rest of us, that the professors started formatting the tests for calculator owners, which forced me and my ilk to make the leap. I paid $135 for my first TI (can’t recall the model No.), mail ordered from California. It took all of my income tax refund and then some.

[Left] Post Slide Rule and Manual

Lafayette Radio Electronics VECTORLOG Model F 686 Slide Rule (top) and example calculation of the hypotenuse of a 3-4-5 right triangle using the P and Q scales.

Donald Ucci, Professor Emeritus at Miami University

I used a Lafayette Radio Electronics (LRE) VECTORLOG slide rule in my undergraduate and graduate studies.  It had specialty scales for vector and trigonometric calculations.  At my university, the EE Department required proficiency in slide rule manipulation.  Students had to pass a slide rule exam to have a B.S. degree conferred.  I studied my LRE manual thoroughly to ensure that I would pass.  As it turned out, I probably over studied as the exam was not as difficulty as I expected.  In any event, I learned how to use my LRE slide rule.  Later in my undergraduate career, I obtained a Dietzgen slide rule and a Keuffel & Esser slide rule and learned how to use them as well.  Using them did pique my interest in nomography; I wondered how the scales were developed and designed to change linear movement into producing nonlinear results!  Image Credits: D. Ucci

[Top Left] Donald Ucci with his college slide rule. The Lafayette F 686 had patented scales (P, P’, Q) for vector computations and Tr1 and Tr2 scales for angle calculations.

James Jefferies, Beta Psi Chapter HKN

I remember being introduced to slide rules in high school.  You could purchase a plastic one, like in the photo, for about a dollar. When I went off to college, my Dad gave me his Dietzgen Model 1738 Decimal Trig, Log-Log also in photos. Wow…roots, squares, exponential, common logs, natural logs, sines, tangents, reciprocals, etc.  I used it all through college and carried it all over campus.  The last time I remember using it was sitting for my professional registration exam in the Nebraska state capitol legislative chamber in 1974. I did not use it much in the work environment as the scientific calculator was introduced in the early 1970’s.

Also in the picture is a CRC mathematical tables book – a healthy companion to the slide rule in education – and a specialized slide rule for audio circuits and a double-sided IEEE conversion tables card from the 1970’s.

James Jefferies with his college slide rule

Steve E. Watkins, Gamma Theta Chapter HKN
Edwin C. Jones Jr., Iowa State University, fostered my interest in slide rules. He donated this Post Model 1460 Demonstration slide rule to the Missouri S&T collection.

Specialty Slide Rule for Pilots. Kane Dead Reckoning Computer and Manual for Aircraft Navigation/Piloting (includes circular and linear slide rule functions) Credit: S. E. Watkins

Mascot carries a slide rule
Joe Miner at the Missouri University of Science and Technology.
Credit: Missouri S&T

William Oughtred (1574-1660)
Credit: Public Domain from Metropolitan Museum of Art

HP 35 RPN Calculator.
Model Introduced in 1972.
Credit: S. E. Watkins