March 20, 2018, Vol. 24, No. 14

Slide Rules Remembered

slide rule

Ah yes – the slide rule. I purchased mine in the fall of 1960, I believe in anticipation of freshman chemistry with Doc Berry. My recollection is that there were two options,and I chose the cheap one. It was manufactured by the Frederick Post Co, model no. 1447. It came in a stiff cardboard case. I still have it amongst my MTU memorabilia! (Pictured left.) I don’t recall how to use it, and my grandchildren are flabergasted that it could possibly have given any information whatsoever.

Ted Reuschel, Forestry, 1964


The picture of the student using his slide rule sure brought back the memories. When I entered MCM&T in the fall of 1963, my Dad presented me with his old K&E slide rule, which he had used when he was an engineering student at the University of Illinois in the late 1930′s. It served me well for the next 15 years or so, until it was replaced with a series of H&P and TI calculators. Does anyone know when Tech students made the switch from slide rules to calculators? I know it was prior to 1977, because when I went back to Tech that year to get my Masters everyone was using calculators.

I have another question: How did we Tech freshman learn to use a slide rule? I have strong memories of large 6 foot long slide rules hanging over the blackboards ( another obsolete technology?) in several of my classrooms during my undergraduate days at Tech, but no memory of any instructor ever using them for a demonstration. I’m guessing that we all picked it up on our own, with a little help from fellow students who already knew how to use one.

Looking at the slide rule today, I was reminded that one was limited to 3 or maybe 4 significant figures, depending on which scale you were using and how much you wanted to kid yourself on how fine you could visually divide the units between the marks on that scale. For calculations which required more significant figures, such as surveying for us civil engineering majors, you had to use Monroe mechanical calculators and 13 place log tables. Talk about the good old days! I can not remember how many significant figures the Monroe’s could handle, but I have vivid memories of dividing the largest number the machine could handle by the smallest number it would take, and watching (and hearing the gears clashing) as the machine took 15 or 20 minutes to perform the calculation. My memory says that we were told not to do this by our instructor, as it was hard on the machines. They would have been better off not mentioning it. I do not think anyone would have thought to do this on their own, but once the idea was in our minds, we all had to try it once just to see it for ourselves.

And what about circular slide rules? I remember a few students carrying them around, but they were much more awkward to carry in your book bag than the straight variety. Am I correct in assuming that they were an attempt to squeeze an extra significant figure out of the device?

I really enjoy your news letter. Keep up the good work.

Peter Gaines, PE 1967, 1978, 1990 (Obviously, I enjoyed going to the Tech)


I completed freshman chemistry with Doc Berry, using a slide rule, in the Fall of 1973.

By the summer of 1974 slide rules were out, and calculators were in.

I still keep a slide rule in my desk at work, and use it occasionally. It is faster and better for some things, and I like the nostalgia.

Hank Missel Class of 1977, Civil Engineering


My wife (Margaret E. “Maggie” Dupuis) named her little hound “PV” while she was studying Chemical Engineering at ‘da Tech’!  Everyone knew this was for her “Post Versalog” slipstick.  (Mostly because we asked her!)

R. Barclay



When I arrived at Tech in the fall of 1968 I had a brand new metal Pickett ”super slide rule” that my high school girlfriend had bought me as a graduation present (knowing I was going to an engineering school). That
thing cost over $200 in today’s money! Nobody had heard of a pocket calculator and the campus computer was an IBM 360-44 that was fed by cards and where you could open a cabinet and see individual memory bits (a small electromagnet connected by visible wires).

In the fall of 1969 in my first chemical engineering class the professor (E.T. Williams) walked around the room on the first day and “passed judgment” on whether your slide rule would cut the mustard for chemical engineering. A number of people who had bought cheap plastic slide rules at the bookstore for freshman chemistry were disappointed when told they wouldn’t be able to succeed without stepping up to a better unit.

In early January 1971 I saw my first calculator (HP 35 that cost $2400 in today’s money) and was stunned. It did logs, exponents, AND trig functions and you didn’t have to figure out where the decimal point was! Plus you
can’t add numbers on a slide rule. Professors resisted allowing calculators in exams because not everyone could afford them but by the time I was in grad school in 72/73 most freshmen had some version of a calculator and the new campus computer system being installed used terminals for data input and programming.

I think it’s fair to say that this was the time when slide rules disappeared from the belts of engineers and computing in general took huge leaps forward.

Kerry Irons


In the 50′s, the trusty slide rule was clipped to your belt, swinging as you walked from class to class. Competition as to who was the fastest slide rule in the west was prevalent. (Lots of westerns on TV at the time)


Professor McMillian and a student run it through it’s paces.

There was one place where slide rules were not permitted, however. Professor McMillian promised an immediate F to anyone found using a slide rule in his Astronomy class. Mathematics was a “pure science” he proclaimed. Instead you had to manually calculate the many spherical trig equations with the help of a five place log table – not exactly “pure” but difficult enough. You couldn’t even use your trusty slide rule to roughly check your result during tests. Interestingly, he also managed the brand new computer lab. A real shortcut, although at the time, probably not a lot more accurate than a slide rule.

Pete Rankin ’59


To this day, I vividly remember my first time walking into Doc Berry’s Freshman Chemistry class during the summer of 1970. Above the Stage (Fisher 101?) was this huge slide rule. I knew instantly that I was in big trouble. I survived, but it was a struggle. I did learn how to use the d… thing and still have one somewhere.

Mark Walter 1975


I still have my Pickett slide rule from high school I bought in 1974 (still with the original leather case, complete with belt loop). I keep it at my office and pull it out from time to time to amuse those younger than me. I think I was probably one of the last classes to be formally taught how to use it. Actually, it’s really an amazing tool.

Patrick T. Hughes, P.E., ECE ’81


Class of ’48, EE and ME, yes, and I still have three slide rules, a Gibson circular, longer scales,  a K & E log log duplex deci trig, and an electrical special I got in the field.

Bob Fricke



I used my Post Versalog slide rule from about 1958 until the HP45 calculator came out in 1973. I was pretty good with the C and D scales, the folded scales, inverted scales and inverted folded scales – never ran off the end of the rule. That rule calculated numbers for Tech classes, Apollo fuel cell components, and jet engine designs. Still have it as a souvenir of early engineering days. (I recently gave another souvenir, my Sault Branch Special drafting set, to my son, who has started a collection of drafting tools.) My boss in those days had a 20” slide rule, with which he could calculate to four significant figures.

Denis Hayner BSME ‘61


I recall everyone carrying a slide rule. either encased on their belt or in their book bag(that’s another relic). I had one professor, I won’t mention names, who had a magnifying glass mounted on his rule and if you didn;t arrive at the same three decimal points that he did you were wrong.! Still have mine. a while back I pulled it out to calculate the number of tiles I would need to retile my roof. My grandkids saw it and couldn;t beleive anyone could be so primitive.

Bill Fish
EE ’57


I was on the “cusp” of the new era of calculators when I was a Freshman at Tech. I initially had a Texas Instruments SR-10 that I had gotten as a High School senior, which only did basic math, square & square root, and reciprocals. I quickly realized that I needed a calculator that a lot did more, like trig functions, exponentials, etc., so I talked my parents into letting me purchase a Hewlett-Packard HP-45 at the campus bookstore. I don’t remember the price exactly but do recall that it was relatively expensive. It was also a radical move because the HP calculators used RPN, or Reverse Polish Notation, which not everyone liked.

Anyway, the Tech memory that goes with this is that Doc Berry prohibited the use of calculators during CH101 exams. You could use calculators during lecture, but if you were caught with a calculator during the exam, you would automatically receive an F. Thus, you had to know how to do all the necessary calculations with a slide rule. This was not overly difficult, but it was definitely cumbersome since other professors had started to allow calculators. By the time I got to my Sophomore year, I no longer had a need for a slide rule. I sold my slide rules on eBay several years ago and actually received a nice price for them (though not enough to compensate for that first HP).

Russ Kerlin

Russ: I remember both those calculators and used them as little as possible.


Dennis, I put my slide rule away after finals. I bought my first calculator to take my P.E. exam and then framed the slide rule with the caption “In case of Emergency Break Glass”. It hangs on the wall above my desk and is a source of amusement for the young engineers.

-Steve Jones BSCE ‘71


I don’t remember much about slide rules and certainly don’t remember how to use one, but I remember when they became extinct.

In the fall of ’72 our Chemistry recital professor told us to not buy an expensive slide rule, but to get a cheap plastic one ($3.00 or so) as they worked well enough and would be obsolete in a year or two. At the time HP was out with the HP 35 calculator that could do all of the slide rule functions and also kept track of decimal places. It was about $400, a very hefty sum in 1972. “Four Banger” (add, subtract, multiply, and divide) calculators were very common shortly after.

Then in 1973, Texas Instruments came out with the SR40 calculator for about $140 that did everything the HP 35 did, and didn’t use the “reverse Polish” entry system. That was the end. The modern equivalent, the TI 30X, is still available at Wal Mart for under $10 and is still the favorite of us old fogies. Most smart phones can do the same thing and so much more.

The Tech bookstore had apparently sold about a thousand Versa Log slide rules at around $25 each to incoming freshmen every year for years and stocked up with the usual order in the fall of ’73. They sold very few that year and were left with crates of leftover ones. They vowed to not sell calculators until the slide rules were gone, so they didn’t carry calculators until 1975 or so when they gave up. I wonder what ever became of the leftovers? One or two should be in a museum somewhere. They did, after all, get us to the Moon.

As a side note, there was a debate among the professors at the time whether or not to allow calculators to be used in tests, the feeling being that they were expensive and some students might be disadvantaged if they couldn’t afford one. Some professors told us to set up our answers using the line-mole method so that all that was remaining was to crunch the numbers. Others used multiple choice and didn’t much care how you arrived at the answer. That disappeared as the machines became less expensive.

The early calculators were battery hogs. A student’s worst fear in life back then was to have the battery go dead in the middle of an exam. Many of us brought spare batteries to the tests.

Bruce Kettunen
Metallurgy ’76


Hi Dennis,
I don’t have any earth shattering experiences regarding my “real” slide rule which I learned to use while attending the Soo Branch of MCMT. However, two of our children were born in Hancock and there was a teething toy introduced called the SLY DROOL if I recall correctly that resembled a slide rule, but was soft and rubbery. We just had to get these and are glad we did because these were as close to the real thing these kids would get as the calculators had taken over big time. Kinda sad when I think back and realize the history I was part of and now the slide rule is probably gone forever. I still have mine though – case and all!

Merry Christmas and Happy New Year!

Fred Roman, BSME ’66

Same to you, Fred. I hope Santa’s good to you.


Both my large Pickett and the small pocket version are still in my drawer and every now and then I’ll break them out to prove to myself I can still use them.

Drives my engineer’s crazy when I can get an answer on the slide rule quicker than they can punch it into a pocket calculator. It really drives them crazy when I do math in my head using the old scientific notation process from my Tech days and tell them they got the wrong answer using the pocket calculator.

Marty Vonk: B.S. Chem. Eng. 1974


The evening before classes started in September 1971 I went to a training session on how to use the slide rule. Still have it and use it for fun every once in a while. Two years later bought my first calculator using the Lay-away method of payment at the downtown office supply store.

Randy Sikkema, PE, BSME ‘77