# 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:** 3
**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, 10:28pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/41 "2015-09-03T22:28:20Z")
> [@CalMeacham](#): > > 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 - Wikipedia](https://en.wikipedia.org/wiki/Nomogram) > > 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. In honor of both science fiction from the pre-digital computer era, and the paper-and-cardboard school of RPGs, the author of the Atomic Rockets site has an entire section dedicated to [Nomograms](http://www.projectrho.com/nomogram/index.html) ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [September 5, 2015, 11:59am UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/42 "2015-09-05T11:59:52Z")
> [@LSLGuy](#): > > 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. Not unauthorized. The changes were submitted and approved by the upstream engineers. And still might possibly have not failed (in spite of the stupid design error), if the hardware had the expected safety margin. Not much the contractors could have done about either problem. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [September 5, 2015, 12:41pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/43 "2015-09-05T12:41:23Z")
> [@LSLGuy](#): > > 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. > [@Melbourne](#): > > Not unauthorized. The changes were submitted and approved by the upstream engineers. And still might possibly have not failed (in spite of the stupid design error), if the hardware had the expected safety margin. Not much the contractors could have done about either problem. IIRC from an analysis I read of the skywalk failure - The original design had one hanger piece from the ceiling going through the beams of both walkways, with a bold below each walkway as support. The design therefore had a 20-foot or so piece of steel rod threaded at both ends and at the center. The obvious question to the engineers then was - Doh! - how do you put a bolt on threads cut in the middle of a smooth rod? As most builders will tell you - “typical engineers!” (Same design on each side of the walkways, so two hangers) Since this minor stupidity was caught when it was time to hang things, the fix was kludged - one hanger from the ceiling to the first walkway beam. The next hanger started from a hole drilled near that hangar and down to the second walkway. SO, you had the full weight of both walkways trying to tear the steel between the two holes on the middle walkway like perforated paper. Apparently, on of the holes was drilled on the point where two beams were welded to make one long one. Slide rules and calculations had little to do with it. The weakness between two holes was a second-order issue - with plain, undisturbed steel each hole was capable of holding the weight. Drill a hole nearby - no. Have a full load of partying patrons dancing too… no. Expect the same strength from a weld seam - not always. ---
**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 5, 2015, 1:02pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/44 "2015-09-05T13:02:32Z")
I’d never paid much attention to the brands before, but it looks like my best slide rule is a Sterling Precision instrument. I also have a couple of Concise circular ones, a matched pair from a company that appeared to change its name from Lawrence Engineering Service to Engineering Instruments, Inc. (or vice-versa), a couple of pocket-sized from Industrial Gauges Corporation, and a behemoth called a Kane Dead Reckoning Computer, which includes a circular slide rule plus a bunch of other rules, charts, and nomograms whose use is a mystery to me. I also have a few other assorted slide charts, mostly pertaining to ham electronics. ---
**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 5, 2015, 1:41pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/45 "2015-09-05T13:41:02Z")
K+E (Keuffel and Esser) is pretty much considered the gold standard of slipsticks. I have a complete set of Log-Log Duplex Decitrigs that I.prize. Even use occasionally… ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [September 5, 2015, 4:49pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/46 "2015-09-05T16:49:12Z")
> [@LSLGuy](#): > > ::: snip :::: > > ================== > 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. This ↑ ↑ ↑ This… I still have & carry my first & only E6B in my flight case. It never runs out of power. 😃 I also have a larger round one that we used to find indicated actual height above ground from our indicated altitude when doing aerial mapping. First electronic calculator I learned/used was an HP-43. What I used for several years. To this day I dislike the ones that have an ‘=’ sign. I have to stop and think about how to use it to get what I want. :rolleyes: ---
**Author:** ![cybersnark](https://avatars.discourse-cdn.com/v4/letter/c/b9e5f3/32.png) [@cybersnark](https://boards.straightdope.com/u/cybersnark)\ **Post date:** [September 5, 2015, 4:54pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/47 "2015-09-05T16:54:26Z")
> [@](#): > > they used a large spiral slide rule wrapped around a tube. Sounds like a Otis King Slide Rule [https://en.wikipedia.org/wiki/Otis\_King](https://en.wikipedia.org/wiki/Otis_King) ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [September 5, 2015, 7:36pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/48 "2015-09-05T19:36:24Z")
> [@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: > Quote: > e to the u, du/dx > e to the x dx > cosine, secant, tangent, sine, > 3.14159 > integral, radical, u dv, > slipstick, slide rule, MIT! > > [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) Far be it from me to point out numbers to MIT folk, but the second line still doesn’t scan. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [September 5, 2015, 8:38pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/49 "2015-09-05T20:38:18Z")
> [@Lumpy](#): > > In honor of both science fiction from the pre-digital computer era, and the paper-and-cardboard school of RPGs, the author of the Atomic Rockets site has an entire section dedicated to [Nomograms](http://www.projectrho.com/nomogram/index.html) Nomograms are wonderful. I remember when I used to read for a books-on-tape organization for the blind I was doing a textbook with a couple of them I had to verbalize. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [September 5, 2015, 9:01pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/50 "2015-09-05T21:01:52Z")
> [@SirRay](#): > > I do know how to read micrometers (but who doesn’t prefer the easy digital readouts?) … When using calipers, I will always take a straight Vernier scale model over one of those silly dial calipers, or a digital one that might need the batteries replaced. Mostly because calipers are not for the ultra-ultra precision work (like you use micrometers for), and the Vernier scale is just so damn elegant. ---
**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 5, 2015, 11:11pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/51 "2015-09-05T23:11:52Z")
For those reading this thread who aren’t familiar with what a Vernier scale is, it’s a rather clever way of increasing the accuracy to which a scale can be read by comparing two offset scales: [Vernier scale - Wikipedia](https://en.wikipedia.org/wiki/Vernier_scale) ---
**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 5, 2015, 11:32pm UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/52 "2015-09-05T23:32:56Z")
Sometimes to an extreme degree: I’ve seen, for instance, a set of calipers capable of measuring to within 1/50 of a millimeter. This, on a device with only one moving part. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [September 6, 2015, 1:25am UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/53 "2015-09-06T01:25:08Z")
> [@Lumpy](#): > > Including the wonderfully clockpunk [Curta Calculator](https://en.wikipedia.org/wiki/Curta) Sometimes dubbed a “math grenade.” I really, really want one. But in good condition they’re in the $1-2k range. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [September 6, 2015, 2:19am UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/54 "2015-09-06T02:19:21Z")
Years ago, I bought a bamboo Pickett like my dad once had, to put next to my computer as a display of anachronism. Not a high-end slide rule, but serviceable and easy to understand. In my uncle’s massive pile of stuff that took us 8 months to clean out, I found a metal Pickett in a hard leather case that nine scales on one side and ten on the other, a few of which elude me. Unlike the bamboo model, there is no A/B, just a square root scale that works the opposite way (double-sided for even/odd orders of magnitude) and a hand dual _π_ scale (C or D times _π_). Kind of bothers me, though: how do you get a number accurately from one scale to another? The whole point of a slide rule is to do all the sequential calculations you can on it before you write a number down, to maintain the analog accuracy. ---
**Author:** ![Kenm](https://avatars.discourse-cdn.com/v4/letter/k/bc79bd/32.png) [@Kenm](https://boards.straightdope.com/u/Kenm)\ **Post date:** [September 6, 2015, 2:52am UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/55 "2015-09-06T02:52:39Z")
> [@Lumpy](#): > > Including the wonderfully clockpunk [Curta Calculator](https://en.wikipedia.org/wiki/Curta) > > > [@Dr.Strangelove](#): > > > > Sometimes dubbed a “math grenade.” I really, really want one. But in good condition they’re in the $1-2k range. The Curta on YouTube: [http://www.youtube.com/playlist?list=PLXujGsmx0YjdCmuv1uLOZaZAHXDEhnzbU](http://www.youtube.com/playlist?list=PLXujGsmx0YjdCmuv1uLOZaZAHXDEhnzbU) ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [September 6, 2015, 2:58am UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/56 "2015-09-06T02:58:33Z")
[If it’s good enough for him …](http://www.nicolamarras.it/calcolatoria/regoli_aeronautici/spock_e6b.jpg) ---
**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 6, 2015, 3:23am UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/57 "2015-09-06T03:23:06Z")
> [@](#): > > Kind of bothers me, though: how do you get a number accurately from one scale to another? The whole point of a slide rule is to do all the sequential calculations you can on it before you write a number down, to maintain the analog accuracy. There should be a sliding reticle with a hairline on it (though this often gets lost on old slide rules). You slide the hair over the number on one scale, and read it on the other scale. ---
**Author:** ![smithsb](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smithsb/32/12107_2.png) [@smithsb](https://boards.straightdope.com/u/smithsb)\ **Post date:** [September 6, 2015, 4:36am UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/58 "2015-09-06T04:36:23Z")
RPI, freshman year 1967. Memories at the “Tute” bookstore. No calculators, too expensive, advantage to the wealthy. A nice new K&E **WITH** the leather case AND belt loop. I can’t remember even the nerds (of which there were many) actually carrying the slide rule on their belt. ---
**Author:** ![kaylasdad99](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kaylasdad99/32/3398_2.png) [@kaylasdad99](https://boards.straightdope.com/u/kaylasdad99)\ **Post date:** [September 6, 2015, 6:07am UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/59 "2015-09-06T06:07:40Z")
> [@Shodan](#): > > Alleged football cheer for MIT - > > _Cosine, secant, tangent, sine, > 3.14159, > E to the X, Q E D, > Slide rule, slip stick, M I T!_ > > Regards, > Shodan > > PS - I had the round one. > [@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) Huh. I first heard about it as a cheer for Cal Tech. _Secant, cosine, tangent, sine; Logarithm, logarithm, hyperbolic sine; 3.14159; Slipstick, slide rule, Tech! Tech! Tech!_ I never learned how to use one, and these days, my sole question about slide rules is: _In what way did J. K. Rowling think a slide rule would assist Barty Crouch in achieving greater precision in trimming his mustache?_ Probably some method only Han Solo would understand… ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [September 6, 2015, 6:21am UTC](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784/60 "2015-09-06T06:21:14Z")
> [@Chronos](#): > > There should be a sliding reticle with a hairline on it (though this often gets lost on old slide rules). You slide the hair over the number on one scale, and read it on the other scale. Yes, I am quite familiar with that thing (never heard “reticle”, we always just called it the hairline). I was just thinking, the advantage to the slide rule was that you could capture numbers on the scale and retain the values in their analogue form through several steps, not losing accuracy until you had to write them down. Then I tried to get the fifth root of 7644 and realized that getting the mantissa onto the C scale to do the division was kind of an exercise in eyeballing the fraction, and then you have to eyeball the resulting fraction (being aware of where the decimal point will be) onto the log scale to get the result. Which, after several mistakes, did turn out pretty close. With the big, double-hairline Pickett slide rule, there are lots of different scales, and sometimes the numbers need to move from one to another in order to do the next operation: every time that happens, the ultimate result will lose some accuracy. [Previous page](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784.md?page=2) [Next page](https://boards.straightdope.com/t/how-did-scientists-and-engineers-actually-use-slide-rules-in-the-old-days/729784.md?page=4)