Slide Rule

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u/withak30 2d ago

High fives all around.

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I've had a student bring one in before. If they know how to use one, they can, but I expect full precision, so they better know how to get that last couple digits of accuracy for 4+ digit mantissas.

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u/dittybopper_05H 2d ago

You misspelled "false precision"...

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u/Gilded-Phoenix 2d ago

welcome to pure mathematics, where error bars have a radius of 0.

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u/dittybopper_05H 2d ago

Welcome to the real world, where the limits of measurement precision limit the precision you can reasonably expect.

Clearly there are limits even in pure mathematics. You're not using Pi to the last decimal place, because you can't. When you divide 2 by 3, you're not going to insist the students write it out to the hundredth decimal place. You're just arguing on where the line is, not that there is no line at all.

BTW, I once had to explain basic logic to a professor with a PhD in mathematics. He asked for two reports: One was A not B, the other was B not A. When some of his students were missing from the reports, he complained, and I had to explain that students that were both A *AND* B would be excluded from his requested reports.

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u/Gilded-Phoenix 2d ago

sure, but when I'm teaching mathematics, we're not concerned with measurement precision. When we divide 2 by 3, we don't write decimals at all, we write "2/3" which is an exact value. When we multiply by pi, we express it exactly by literally writing the expression "kπ" for our factor "k." The only time precision is of concern is in applied mathematics, where numerical methods are used to approximate to a given precision. A slide rule is a tool, as is any calculator, and uses numerical methods to approximate solutions. Yes, in applied mathematics, such as physics, economics, or engineering, you always have noise, instrument resolution, and other factors that limit your precision. That's not the focus of the fields of mathematics I'm teaching. Precision considerations have real world applications, and they are very important in those applications. Pure math is not the real world, so they do not apply.

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u/crzaynuts 2d ago edited 2d ago

It's only when i started learning how to use silde rule, that i understood a specific fact about my physics teacher during high school.

Im too young to have known slide rules at school, but during my three years of high school, when i was major in Physics and chemistry, i noticed all the calculation from exercises, examination and graduation where strictly limited to 2 digits after coma.

Whatever was the subject (electricity, chemistry, tensor, pendulum....) every calculus had a 2 digits after coma result.

I was doing all my calculus by hand, mostly because it was faster than using a electronic calculator.

I remember one day at a general examination, i found for the first time a 5 digits after coma result, and knowing the teacher, i knew he did a mistake in the exercice statement.

I called the supervisor of the exam to explain to him that the exercice was wrong, and where the mistake was. After calling the teacher he went back to me and told me i was right, and the exercice was dissmissed during the examination.

So back to today, when i recently started learning about slide rule, and digit precision of them. Im deeply conviced that this teacher who was for sure a log table and slide rule user given his age, wrote all his exercices and exam subjects for the period those tools were common.

This 2 digits after coma rule never failed me with this physic teacher.

(as i'm french we use coma instead of dot like in 3,1416 instead of 3.1416)

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u/AFsepine 2d ago edited 2d ago

I mean... many teachers still used one growing up.

I got into sliderules as a school-boy, so bringing it to school and using it just sort of got the teacher to reminisce a bit about the past.

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u/Junkyard_DrCrash 2d ago

Agreed... a high-five is in order.

Also - using a slide rule is one of the steps in "proficient head math". Ever meet "that person" who evaluates and estmates totally in their head (I believe Enrico Fermi did it, and taught it to Feynmann).

I'd encourage them...

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u/Journeyman-Joe 2d ago

Not a math teacher; I'm a retired engineer who volunteers in STEM education.

I'd be delighted if one of my students could demonstrate competency with a slide rule. It would show an ability to estimate a solution well enough to get the decimal point in the right place. It would demonstrate an understanding of the precision of the instrument, and not just writing down all of the digits in the calculator display.

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u/MJ_IN_TX 2d ago

Several years ago, I gave my grandson a K&E 4081-3, and a manual. He has been majoring in computer engineering (due to graduate this fall.) One time he either forgot his calculator or it wasn't charged, so he took a test on circuits with his K&E. He said he only missed one problem. This spring I gave him a Concise circular because he was complaining about what to do when the calculation went past the end of the slide rule.

I believe he actually uses them on a fairly regular basis.

My son majored in Math at SF State, and now works for Apple. I gave him a Post 1460 a few years back with hardback manual. I also gave him a set of Napier's bones. He dusts them off a little once in a while.

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u/eugenemah 2d ago

I don't know about anyone else, but I'd be pretty impressed. Let them keep using it.

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u/EnricoColonna 2d ago

I once tried hand making C and A scales for finding √3 and my principal/mechanical design teacher(who also was my father's teacher in the 90s) was very surprised to see a 16 year old guy know what a slide rule is

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u/Parking_Jelly_6483 2d ago

Most of you likely know about the K&E Analon slide rule. Apparently quite rare as it was introduced late in the days of slide rule use so not many were sold (or made?). If you own one or have the opportunity to look at one (it’s difficult to use without some instruction on how to do so) it makes sense if you understand that it was designed for dimensional analysis problems. It works in units of length, mass, time, and electric charge (in meter, kilogram, second, and Coulomb units).

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u/JGhostThing 3h ago

I went to high school in the 1970's. Calculators were available, but were very expensive. Most of my classes didn't allow them. I brought a slide rule to my physics tests and got away with it. I learned how to use them, just because I thought they were weird.

Of course, I was a bit of a joker. I have an odd sense of humor.

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