# How did scientists and engineers actually use slide rules, in the old days? **URL:** \ **Category:** Factual Questions\ **Created:** [September 3, 2015, 4:37am UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784 "2015-09-03T04:37:48Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [September 3, 2015, 2:58pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/21 "2015-09-03T14:58:05Z")
> [@Monty](#): > > [Here](http://www.antiquark.com/sliderule/sim/virtual-slide-rule.html) is one of my favorite sites. I use it occasionally when I feel “old school”. You can also refer to your calculator as “an electric slide rule”. 🙂 Mine actually was my dad’s, so it dated back to the 40s. It was full of functions, many of which I never used. ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [September 3, 2015, 3:04pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/22 "2015-09-03T15:04:07Z")
I think the disconnect in understanding here might be that anyone who grew up with computers is used to a machine that does all the work - you basically ask it a question and it applies all the factors necessary to give you an answer. In the calculator and slide rule era, the machine between your ears did all the work, with the assistance of a tool that made the component calculations easier. ---
**Author:** ![Dendarii\_Dame](https://avatars.discourse-cdn.com/v4/letter/d/bbce88/32.png) [@Dendarii\_Dame](https://boards.straightdope.com/u/Dendarii_Dame)\ **Post date:** [September 3, 2015, 3:07pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/23 "2015-09-03T15:07:19Z")
My husband (who is **Andy L** ) had a friend in high school who said, “Here’s a slide rule. I can’t figure out how to use it. Can you show me?” My husband looked at it. “The reason you can’t figure out how to use it is that this is not a slide rule. This is a metric converter.” (He did offer to show the guy how to use a slide rule if he provided one.) Robert Heinlein had a character nicknamed “Slipstick” because he was so quick with mental calculations. ---
**Author:** ![Bert\_Nobbins](https://avatars.discourse-cdn.com/v4/letter/b/aeb1de/32.png) [@Bert\_Nobbins](https://boards.straightdope.com/u/Bert_Nobbins)\ **Post date:** [September 3, 2015, 3:19pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/24 "2015-09-03T15:19:09Z")
> [@Francis\_Vaughan](#): > > Something that I liked about the discipline of using a slide rule was that you had to do your own decimal place calculations. So you got to grips with orders of magnitude very quickly, and you got good at sanity checking calculations. Something that was lost with calculators. It remains altogether too easy to mess up with a calculator and not twig to a miss-key or similar error. To me that’s the downside of slide rules. You have to keep track of the decimal point all the time, and not just do a sanity check at the end. Having said that, I will never let go of my beautiful Faber-Castell log-log rule, until you prise it… etc etc. Good enough to get a degree with, back in the day. I got a scientific calculator as soon as the price got reasonable- a trusty Casio FX-19, which I still use. [http://www.calcuseum.com/poc\_08081.html](http://www.calcuseum.com/poc_08081.html) I had no truck with programmable calculators. I waited until the Acorn Atom came along.[https://en.wikipedia.org/wiki/Acorn\_Atom](https://en.wikipedia.org/wiki/Acorn_Atom) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 3, 2015, 3:20pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/25 "2015-09-03T15:20:47Z")
> [@](#): > > Robert Heinlein had a character nicknamed “Slipstick” because he was so quick with mental calculations. Who was also Andy L. (that is where your husband got his username, right?) At the museum where I work as a day camp counselor, one of the exhibits is John Glenn’s slide rule, that he took with him on his historic flight. I always tell my campers what it is, and that it’s my favorite exhibit. I’m just waiting for one of them to ask how to use it, and I always keep one in my bag against just that question. ---
**Author:** ![Claverhouse](https://avatars.discourse-cdn.com/v4/letter/c/13edae/32.png) [@Claverhouse](https://boards.straightdope.com/u/Claverhouse)\ **Post date:** [September 3, 2015, 3:31pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/26 "2015-09-03T15:31:40Z")
So, having no opinions on slide rules, I looked up the creator, the [**Rev. William Oughtred**](https://en.wikipedia.org/wiki/William_Oughtred), and of his quarrel with the King’s Tutor in Mathematics, and Quartermaster General, his ex-pupil, [**Richard Delamaine the Elder**](https://en.wikipedia.org/wiki/Richard_Delamaine) ( I have no idea why a King would want a maths tutor; however all these old mathematicians seem to have been good royalists, and admired by their monarchs for some reason ); and that led to the [**Rev. Edmund Gunter,**](https://en.wikipedia.org/wiki/Edmund_Gunter) who invented Gunter’s Rule ( ‘_generally called the “Gunter” by seamen_’ ) , Gunter’s Quadrant, and Gunter’s Chain. Which chain was 66’ for measuring land. I had no idea a chain measurement was so recent in origin. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [September 3, 2015, 3:49pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/27 "2015-09-03T15:49:08Z")
> [@Amateur\_Barbarian](#): > > I think the disconnect in understanding here might be that anyone who grew up with computers is used to a machine that does all the work - you basically ask it a question and it applies all the factors necessary to give you an answer. > > In the calculator and slide rule era, the machine between your ears did all the work, with the assistance of a tool that made the component calculations easier. There was an excellent article in the old _American Heritage Magazine of Invention and Technology_ about just this topic, using the example of a slide rule vs. the electronic calculator as an old-school tool that required knowledge and skill to use vs. the modern tool for les-skilled or unskilled workers. Another example they cited were the drawhorse vs. a battery of pre-set mechanical drills, lathes, saws, etc. (such as the sort of assembly-line system used for making nautical “deadeyes”) ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [September 3, 2015, 5:21pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/28 "2015-09-03T17:21:22Z")
> [@CalMeacham](#): > > Slide rules gave you a quick way of multiplying numbers together, raising numbers to second and higher powers, taking square and cube roots (and other roots, too) and doing trigonometric calculations, all to three-place accuracy. What it didn’t let you do was add or subtract (although there were mechanical devices for that, if you wanted, including the abacus and various ingenious yet simple devices). Including the wonderfully clockpunk [Curta Calculator](https://en.wikipedia.org/wiki/Curta) ---
**Author:** ![BrotherCadfael](https://avatars.discourse-cdn.com/v4/letter/b/977dab/32.png) [@BrotherCadfael](https://boards.straightdope.com/u/BrotherCadfael)\ **Post date:** [September 3, 2015, 5:22pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/29 "2015-09-03T17:22:28Z")
> [@John\_Mace](#): > > My HS physics teacher made us use one. This was 1972 and TI calculators were just hitting the consumer market. I actually used one all thru college, but we never used numbers all that much in physics. (My HS teacher purposely made us use actual numbers so you couldn’t do the tests without a slide rule.) So, you and I are of the last generation that were required to learn to use a slide rule. My HS chem teacher insisted we all use a slide rule, even if you owned a calculator (four-bangers were down to about $35 by then), because, obviously, calculators were only a fad. My dad, an electrochemical engineer, bought me a calculator for college. We once set up some test problems, and he used his slide rule and I used the calculator. He beat me to the answer every time. ---
**Author:** ![SirRay](https://avatars.discourse-cdn.com/v4/letter/s/cc9497/32.png) [@SirRay](https://boards.straightdope.com/u/SirRay)\ **Post date:** [September 3, 2015, 5:27pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/30 "2015-09-03T17:27:40Z")
I am an electrical engineer, middle aged, and never once until this thread heard the term “Slipstick” for Slide Rule. I have seen slide rules, even sort of knew how to use it, but we didn’t near to learn it in early '80s High School ('cause we all had our TI-55s on our belts…well, the women didn’t, but us nerds did). I do know how to read micrometers (but who doesn’t prefer the easy digital readouts?) and have several of those specialized “passive” analog calculator from decades back (like the cardboard wheel to look up the amount of concrete you need for a given project) that hardware stores and lumber yards used to give out (I’m sure there were specialized ones for electronics too). I forgot how to use a slide rule because, quite frankly, I’ll take the small solar powered calculator over a slide rule any day (and it’s successor, the smartphone calculator app). ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [September 3, 2015, 5:30pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/31 "2015-09-03T17:30:34Z")
I have to share a cartoon I saw in the '70s. An angry-looking slide rule is glaring at a puzzled-looking calculator. The slide rule says, 'Just wait ‘til your dry cells run out, Speedy!’ ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [September 3, 2015, 5:34pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/32 "2015-09-03T17:34:21Z")
> [@CalMeacham](#): > > There was an excellent article in the old _American Heritage Magazine of Invention and Technology_ about just this topic, using the example of a slide rule vs. the electronic calculator as an old-school tool that required knowledge and skill to use vs. the modern tool for les-skilled or unskilled workers. A while back I read an article by an engineering professor who straddled the old and new worlds, and was expressing the concern that computerized engineering would lead to intellectual distance and errors or failures. His notion was that engineers who worked directly with the specs and layouts and calculations would have an inherent “feel” for when something was wrong, and look for the problem. Newcomers who came into the field relying on computers to do all the grit work and hard thinking would not have that sense, and a grievous error in programming, reference databases, problem setup or the like could lead to dangerously incorrect results - results that no one would know was wrong because they didn’t have that “hands on the steel” intuition and had come to assume computers were always correct. I really don’t know how this has played out in the last 25 years or so, other than to look at civil engineering failures like the Hartford arena, KC hotel skywalks, various buildings that have collapsed during construction, etc. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [September 3, 2015, 5:49pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/33 "2015-09-03T17:49:13Z")
> [@Amateur\_Barbarian](#): > > A while back I read an article by an engineering professor who straddled the old and new worlds, and was expressing the concern that computerized engineering would lead to intellectual distance and errors or failures. > > His notion was that engineers who worked directly with the specs and layouts and calculations would have an inherent “feel” for when something was wrong, and look for the problem. Newcomers who came into the field relying on computers to do all the grit work and hard thinking would not have that sense, and a grievous error in programming, reference databases, problem setup or the like could lead to dangerously incorrect results - results that no one would know was wrong because they didn’t have that “hands on the steel” intuition and had come to assume computers were always correct. > > I really don’t know how this has played out in the last 25 years or so, other than to look at civil engineering failures like the Hartford arena, KC hotel skywalks, various buildings that have collapsed during construction, etc. I don’t know about use of computers causing failures. I think that it does, however, make you think about problems in different ways. One example – pre-computer, people used nomograms a lot. Nomograms help give you a good visceral 'feel" for solutions that you don’t get from simply plugging them in to the equations > **[Nomogram](https://en.wikipedia.org/wiki/Nomogram)** > > A nomogram (from Greek νόμος (nomos) 'law' and γραμμή (grammē) 'line'), also called a nomograph, alignment chart, or abac, is a graphical calculating device, a two-dimensional diagram designed to allow the approximate graphical computation of a mathematical function. The field of nomography was invented in 1884 by the French engineer Philbert Maurice d'Ocagne (1862–1938) and used extensively for many years to provide engineers with fast graphical calculations of complicated formulas to a practi... There used to be entire books devoted to making nomograms. Today, it’s a lost art. But I get a better feel for object/image/magnification relationships from the relevant nomogram than from the formulas. Something else neat about slide rules – the relative area occupied by each digit in te slide rule is the probability for that digit appearing first in any table of frequencies of first digits, from lists of, say, populations, or of lengths of rivers. In other words, the width of a number on a slide rule gives you the Benford Probabilities for those digits. The fact that it doesn’t matter what units you use to measure the lengths of rivers, or coastlines or whatever leads directly to this result. The fact that the Benford Probabilities are unchanged by multiplication of all quantities by the same factor gives this distribution – it’s the only one unaffected by multiplication. > **[Benford's law](https://en.wikipedia.org/wiki/Benford%27s_law)** > > This is an accepted version of this page > > > Benford's law, also known as the Newcomb–Benford law, the law of anomalous numbers, or the first-digit law, is an observation that in many real-life sets of numerical data, the leading digit is likely to be small. In sets that obey the law, the number 1 appears as the leading significant digit about 30% of the time, while 9 appears as the leading significant digit less than 5% of the time. Uniformly distributed digits would each occur about 11.1% of t... ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [September 3, 2015, 6:27pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/34 "2015-09-03T18:27:07Z")
> [@CalMeacham](#): > > Close – it was > > _e to the u du dx > e to the x dy > secant, tangent, cosine, sine > 3.14159 > (something, something) > Slipstick Slide Rule > MIT!_ > This site gives the following, to fill in the gap in my memory: > > [http://www.anvari.org/shortjoke/Science\_Humor/1106\_other-cheers-e-to-the-x-dx-dy-radical-transcendental-pi-secant-cosine-tangent-sine-3.html](http://www.anvari.org/shortjoke/Science_Humor/1106_other-cheers-e-to-the-x-dx-dy-radical-transcendental-pi-secant-cosine-tangent-sine-3.html) When I was there it was closer to Shodan’s version, but instead of QED, it was du/dt. (which makes more sense) I think it is one of the songs I published in the Baker House newsletter when I was the editor of it, so I’ll look it up. There is also the verse of “We are the engineers” with the engineer sitting with the girl One hand worked the slipstick While the other hand traced the curve. ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [September 3, 2015, 6:30pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/35 "2015-09-03T18:30:37Z")
> [@Dendarii\_Dame](#): > > Robert Heinlein had a character nicknamed “Slipstick” because he was so quick with mental calculations. Slipstick Libby for those of you did not read Methusaleh’s Children and the short story starring him, whose name I forgot. Astounding had a cover in about 1954 with a sliderule over a spaceship. The story it illustrated involved the crew on a spaceship needing to create a perfect square wave. Oh, for the days of stories with true social significance. (Could this have been what the New Wave was really about?) ---
**Author:** ![missred](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/missred/32/14096_2.png) [@missred](https://boards.straightdope.com/u/missred)\ **Post date:** [September 3, 2015, 6:49pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/36 "2015-09-03T18:49:30Z")
> [@John\_Mace](#): > > You can also refer to your calculator as “an electric slide rule”. 🙂 > > Mine actually was my dad’s, so it dated back to the 40s. It was full of functions, many of which I never used. The Electric Slide Rule sounds like a dance. 🙂 ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [September 3, 2015, 6:51pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/37 "2015-09-03T18:51:02Z")
> [@Voyager](#): > > Slipstick Libby for those of you did not read Methusaleh’s Children and the short story starring him, whose name I forgot. “MIsfit.” Don’t forget that Lib was transgender and transformed into a woman in one or two of the very late novels. Slide rules figure fairly prominently in Heinlein stories through at least Have Space Suit… might have shown up in a couple of the last short stories in the early 1960s but I can’t recall for sure. ---
**Author:** ![Mk\_VII](https://avatars.discourse-cdn.com/v4/letter/m/5f9b8f/32.png) [@Mk\_VII](https://boards.straightdope.com/u/Mk_VII)\ **Post date:** [September 3, 2015, 7:08pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/38 "2015-09-03T19:08:58Z")
I had a 12" Blundells of Luton one which my father had bought just after the war. It was made of Bakelite with a glass graticule and came in a heavy Bakelite case. I also had a 6" one that you kept in your jacket pocket at school. And when grandfather’s house was cleared out I got a very sophisticated British Thornton one of fairly recent make which I don’t think had ever been used. But calculators were starting to come in, even then, though they were heavy, clunky, and some used Reverse Polish Notation which you had to get used to. ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [September 3, 2015, 7:30pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/39 "2015-09-03T19:30:54Z")
> [@Amateur\_Barbarian](#): > > “MIsfit.” > > Don’t forget that Lib was transgender and transformed into a woman in one or two of the very late novels. > > Slide rules figure fairly prominently in Heinlein stories through at least Have Space Suit… might have shown up in a couple of the last short stories in the early 1960s but I can’t recall for sure. Thanks. I read those stories before I owned a slide rule. I don’t recall another reference, but it is certainly possible. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [September 3, 2015, 9:40pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/40 "2015-09-03T21:40:03Z")
> [@Amateur\_Barbarian](#): > > … I really don’t know how this has played out in the last 25 years or so, other than to look at civil engineering failures like the Hartford arena, KC hotel skywalks, various buildings that have collapsed during construction, etc. The KC hotel skywalks were designed & engineered correctly then built wrong when the fabricators made an unauthorized change to simplify building the design. Not sure there was much the upstream engineers could have done. ================== I still carry my pilot’s circular slide rule in my work briefcase / tool bag. I haven’t used it in flight in about 15 years; not since I started flying the more computerized airplanes. But I’ll carry it until I retire. I pulled it out at home a few weeks ago and was disappointed to see how many of the advanced functions I couldn’t remember how to operate. Not that those calcs were used very often back in ye Olden Dayes. [Previous page](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784.md?page=1) [Next page](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784.md?page=3)