First experience with a slide rule


Hello, what I'll say maybe will sound for you almost obvious but for a newbie like me it's like a personal discovery
When I was a student infact, the slide-rule, at that time, had been already replaced with the first electronic calculators, since a few years. Inspired by a lot of posts in matter on MoHCP, I wanted to enjoy myself imagining the benefit of the people who tried the first time the HP35 in place of the slide-rule.
I found one of them, I read the istructions and I tried to use it for simple calculations and I found that for not skilled people it's very hard and complicated to do it, expecially for people like me who have not still good eyes like in the youth!!
In approximation and parallaxes errors it's easy to throw away all the enthusiasm and the faith!!


There shouldn't be any paralax, as the hairline on the rear surface of the glass gets pressed down against the rule. If it's well made and not out of adjustment, you can usually (depending on the function) get at least three digits of accuracy, sometimes more. Although it may be hard to believe for someone who's used to anywhere from 10 to 20 digits on a calculator or computer, 3 is actually plenty for a large portion of engineering work.

When trying to show a beginner, something I always see is their frustration with trying to get an exact adjustment on either the slide or the cursor. There's a way to hold it to get the effect of a vernier as your roll your fingers. It occurs to me now there's probably a way I could illustrate that on my slide-rule page,

There were the cylindrical rules (see which had scales 50 times as long, wrapped around a cyclinder to make the size manageable. I've never seen one in person, let alone used one, but it looks like you would normally get 4-5 significant digits; but it did not have all the scales that a normal slide rule had.

Vision is of course necessary, but corrective lenses should take care of that for most people. I'm nearsighted, and even at age 53, it's only a small exaggeration to say I can see germs at 6" (15cm) without glasses.

In the 1970's after all my classmates had gone to calculators, I kept using a slide rule for a few more years because I could see its value in helping understand number relations. Even today, when discussing something with the other engineer I work with, I do the decibel conversions (requiring the common logarithm) instantly in my head, and he says, "How do you do that so fast?" I replied, "You're just slightly too young to have used a slide rule, huh?!" I went to a calculator when I needed something programmable, a requirement the slide rule could never meet. First I got a TI-58c, then a TI-59, then the HP-41cx.

Edited: 12 Aug 2013, 1:51 p.m.


That SIC 4500 4" slide rule is cute!

I've never seen one in person

Matthias Wehrli showed us his model at the Allschwil's Meeting 2008.

Kind regards



Thank-you Garth for your reply.
I've been on your page and it's very interesting and full of other interesting links.
I've admiration for the slide-rules and respect, just I would talk about my difficulties in using them. I'm 52 years old and I started wearing glasses just a few years ago, but believe me if i say that to read numbers on the scale it's for not so easy for me, even with lenses.
I have maybe to thank for this all the time I spent in the last 15 years every day with personal computers.



I missed the slide rule era by just one year. Several years ago I bought my first SR, an Aristo Studio and since then collected quite some interesting models.

You need a good book (and glasses) to learn all the tricks. I managed to get a book covering SRs in great detail and some electronic calculators like the HP-65. Unfortunately it's german, but of course there will be something in your preferred language :-).


Have a look at (garth has linked it on his website as well).there you can find lots of instructions, manuals and a good coursemon how to use the SR.


Hi aurelio,

a few months ago my interest in sliderules was revived again (after more than 40 years), and I searched the internet for sites about this stuff. Within a few days I've collected the most interesting material about sliderules and I've made a comprehensive sliderrule package out of it.

If anyone is interested - here's my Sliderule-Package (about 10MB):

Other link:

It contains:

1) Sliderule-Introduction.chm and Sliderule-Calculations.chm: basic informations for those who aren't familiar with sliderules at all

2) very simple sliderule and a abacus program

3) and two different sliderule simulators (201 is much better)

4) a Java-applet simulator (runs only in a browser)

5) SlideRule-Simulations.chm and Aristo-Multilog.chm: 11 different sliderule simulations (written in JavaScript). I've collected them from different websites, put them all together into one single HTML-file and compiled it as CHM-file, so it can be used without a browser (just like any other help-file)

6) and
these 2 are the top-programs, very comfortable and full of features, and you can even create your own sliderules!

And here are 2 links to very good sliderule introductions/informations:

or as 5MB PDF-file ("SlideRule Course"):

and a quite large (27MB) PDF-file "All About SlideRules":


Edited: 13 Aug 2013, 5:06 a.m.


So, we have a big thing in common! I have several slide rules, most NIB, and have sold many duplicate NIB as well.

Supplementing your tips: When using them, remember that most calculations are adding logarithms. That helped me before calculators and it still helps me today! Also, remember that the "I" scales are the inverses so think in terms of x * (1/y)--I like how K&E's book explains it!

When students are converting from the exponential form to the logarithmic form, the slide rule helps bring alive the concept and its usages.

When doing a lot of ratios, I still break out the slide rule because, for 3 or 4 digit accuracy, it is still faster than using a machine. The instruction books usually call those tables. Since the Law of Sines is actually ratios...

Do you remember tweaking your slide rule calculations with log tables?

Edited: 13 Aug 2013, 6:43 a.m.


thank-you fhub, thank-you Ingo for your precious informations and links


I came to school well after the slide rules. I fun them fun to use, however, I need a calculator to verify that I got the right answers.


It did require you to have an approximate idea of what the answer should be, especially in regard to where the decimal point is, although it would also help catch if you used the wrong scale. Today's kids would take any answer that comes from the calculator as truth, even if it's way off because they entered the wrong inputs or did the wrong operation.


Garth -- You're absolutely right about kids blithely believing anything the calculator says, but it's not just kids, it's everybody. HP did a study 'way back in the HP-65 days (most HP Museum regulars have probably heard this story already) in which both students and professionals were given HP-65's to use on a battery of math problems. Unbeknownst to these unwitting guinea pigs, the HP-65's were programmed to generate incorrect answers every so often, sometimes slightly off, and sometimes wildly off the mark. HP wanted to see how bad the answers would have to be before they were recognized as incorrect.

To HP's dismay, NOBODY caught ANY of the incorrect answers. Everybody simply wrote down the displayed result and moved on to the next problem!

I tell my students this story every year, and warn them that I might do the same to their required HP 50g's. (It would be a lot easier to do on a 50g than on a 65!) I haven't needed to actually do it, however, because the story and the warning seem to suffice.

If anybody knows a link to that HP-65 story (I hope it's not apocryphal!), please share it. Thanks!




I would find it most interesting to hear what uses you make of the HP-50g in your classes, and how its particular properties are useful. I can think of many questions, but you can undoubtedly think of many things to talk about without prompting from me.

Not to get off the topic of slide rules, though: if you were amenable to such a suggestion, you might make it a new topic.


Actually, more on topic, I half-jokingly recommend that my students replace their HP calculator with something far better for learning: the Sama & Etani 600-ST. I hope you enjoy my description of it, written back when the hamster-butt-ugly HP 49G ruled the roost.



Speaking of a circular slide rule-- Howard Speegle, founder of Diva Automation, told me this last week (He gave me permission to copy it here):

With your background, you might enjoy some aspects of my work on the Nimbus weather satellite. It had a 250 mW transmitter and our 85-foot dish with Maser amplifier could achieve autolock at -150 dbm at a range of 3000 miles.

However, the launch vehicle suffered an early burnout and the orbit was degraded, causing the satellite to be lost to the free world for three days. No one at NASA Goddard or the DEW line or any tracking stations around the world were able to locate any evidence that it existed. We scanned the skies continuously in every sort of random and geometric pattern for days, but no cigar.

Finally, I whipped out my trusty circular pocket slide rule and did a bit of jimjam combined with whazzamatazz and came up with a reasonable approximation of what the orbit would look like with a 10-second premature shutoff and suggested to my boss that they point the antenna in a certain direction at a certain time.

And lo!, it came to pass. He wanted to know where I had studied astrophysics and I didn't think he would appreciate knowing about my plastic slide rule so I simply shrugged it off.

A few weeks later, the ham club at the University of Alaska, down the road, timidly asked if we might have any interest in the telemetry tapes they had made of the first pass. A bunch of kids using a hand-pointed chicken wire parabola had made beautiful recordings of the entire pass and subsequent passes. They had outperformed the combined might of NASA and the millions upon millions of dollars of state of the art equipment we had. Kudos to them. I don't know whether we ever thanked them. Perhaps I should send this story to the university so they can add it to their list of accomplishments.



I assume YOU have the FULL array of the many available INSERTS? I still have my Sama & Etani - w inserts (went to Afghanistan w me). If memory serves me, you have made this presentation in the past, yes? BEST!



I assume YOU have the FULL array of the many available INSERTS?

No, just the ST insert, although Bob Prosperi emailed me scans of the CE insert recently (thanks, Bob!). I'll add them to my S&E web page. Can you send me scans of the other inserts? It'd be cool to have them all available on that page!



This URL

has good scans of assorted inserts. I believe I have at least one duplicate, maybe more, inserts. Happy to donate when I find. Thanks for the reminder of the 'old days' of computation. BEST!



I used to travel with a small circular slide rule to convert foreign currencies: with a glance at the disc I could tell the price in CHF.

hamster-butt-ugly HP 49G

I think you forgot frozen here. At least that's how I imagine it turned blue.




Actually, more on topic, I half-jokingly recommend that my students replace their HP calculator with something far better for learning: the Sama & Etani 600-ST.


In 11th grade I got my first slide rule: a Sama & Etani Model 700 with the MM insert and a genuine leather carrying case. Didn't get an electronic calculator till Christmas of 12th grade. I still keep the slide rule in my drawer. The calculator died long ago.

I did a fun session last year with the other teachers in the dept showing them how to use a slide rule. One right out of college said, "You really have to know your math to use these." Couldn't have said it better myself.

-Wes Loewer


I've been growing up with pocket calcs not knowing slide rules for many years. During an exam in physics in school my teacher pointed me into the right direction by criticising the high precision figures that I read from my calc. He then introduced the course to the difference between precision and accuracy and how to deal with that in everyday physics problems.

At that time this wasn't and as far as I can tell: still isn't taught in schools. With my recent interest in slide rules I now have fun declassing the ubiquitous smart phone calc users to be faster with a slide rule with sufficient precision (and most of the time higher accuracy as they more often than not don't get the order of magnitude right). And if it's getting more complex (sic!) I have my HP15C in my pocket.


It did require you to have an approximate idea of what the answer should be, especially in regard to where the decimal point is, although it would also help catch if you used the wrong scale. Today's kids would take any answer that comes from the calculator as truth, even if it's way off because they entered the wrong inputs or did the wrong operation.

I agree. Keeping track of the decimal point is a must when using a slide rule.

I usually do calculations again if the answer doesn't seem right. I think that is from habit and a good math sense though.


Today's kids would take any answer that comes from the calculator as truth, even if it's way off

I pointed this out to my physics class when somebody got an answer that a car going 60 mph would stop in 1e-4 meters when the brakes were applied!

To Ingo:

He then introduced the course to the difference between precision and accuracy and how to deal with that in everyday physics problems.

At that time this wasn't and as far as I can tell: still isn't taught in schools.

I don't know about (US) high schools, but in college physics that was emphasized (at least by me) from day one! We even had a lab session on measurement accuracy versus precision and all subsequent lab write-ups were expected to include comments about accuracy of the results.


I spent $35 in 1969 (equivalent to $230 in 2013) for my first and favorite scientific slide rule, the Dietzgen N1725 Microglide, which remains 44 years later still the finest slide rule that I have ever seen.

It was essential when I studied EE at Georgia Tech, where I graduated in 1974. Even though the HP-35 had been around for two years at that time, and the HP-45 for more than a year ($400, equivalent to $1900 in 2013), the high prices kept all but a few from digital calculator use.

I then entered submarine nuclear propulsion training in the U.S. Navy, where slide rules were also mandatory. As part of that training, I received the best course in slide rule usage, including tricks and shortcuts, that I ever saw...far better than anything I got at Georgia Tech. Few ensigns could afford an HP calculator on their $7200 per annum military pay. The TI SR-50 had a late-1974 street price of $125 (equivalent to $600 in 2013) so even TI machines were rare.

Slide rules were very important well into the mid-1970s. When I entered Georgia Tech in 1970, a decent slide rule was the only computational device that a student was expected to have.

Edited: 14 Aug 2013, 4:50 p.m.


Hi Mike, I read with admiration about your experience with the slide-rule, and I can imagine people who grew up, studied and worked with them like Spartans in the ancient greece, they where stronger than others 'cause of heavier swords used in training in place of the standard used in battle...

Even today a student who could have a course in slide rule usage, including tricks and shortcuts, togheter with PC or calculator, could be like a Spartan of the modern era


I got my first slide rule, a Post Versatrig, a gift from my Mom, who taught me to use it in my high school math and physics classes. 1963 or thereabout. I've always preferred the feel of a bamboo slide rule. When I went to Michigan State in 1965, the first class I taught (as a freshman student, non-credit) was to other students, "How to use a Slide Rule". My favorite was the VersaLog II, most used was a 5" version, the 1461.

I think it has to do with the mechanics of working and observing a slide rule, as opposed to the mechanics of pushing buttons and watching a display. I can work a calculator by touch, but not a slide rule. There's more mental interaction with the slide rule. I think this leads to a different understanding of the mathematics being done; the slide rule user is shoveling sand with a shovel, the calculator is shoveling sand with a backhoe. You can get identical results, but the former is more involved in the process. (The fancy term is kinesthetic or tactile learning.) Even if you are not a primarily K/T learner, the process itself does shape your understandings. Having to keep track of decimal points adds to the mental involvement in solving the problems.


I think I may be among the last (youngest) to have used a slide rule in school. When I was in 11th grade Chemistry in 1979-80, the teacher explained that the Austin, Texas school district had a policy that unless everyone in the class had a calculator, no one could have a calculator. Therefore, we were all required to use slide rules.

The next year I continued to use my slide rule in trig and physics, but some students had calculators. So either the district dropped the policy, or maybe our Chem teacher just didn't want us to have calculators. It sure made significant figures a lot easier to deal with. :-)

I got a calculator that Christmas, then moved to a different school where nobody used a slide rule.



Wow, I thought I was the youngest. I began dropping the slide rule when I needed something programmable and got a TI-58c in Dec '81. I didn't drop it all at once. I was the only one with a slide rule in the high-school physics class in the '77-'78 school year, and the other guys initially thought it had to be slow and very inexact. They gradually had to drop the slowness argument, but the cool thing with the accuracy came when the teacher told everyone that my answer for the time a satelite took to orbit the earth in one of the problems was only four seconds different from his which he got on his calculator.

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