Know How To Use a Slide Rule?

high_rolla writes "How many of you have actually used a slide rule? The slide rule was a simple yet powerful and important tool for engineers and scientists before the days of calculators (let alone PCs). In fact, several people I know still prefer to use them. In the interest of preserving this icon we have created a virtual slide rule for you to play with." Wikipedia lists seven other online simulations.

Comments

I learned how to use my slide rule...

[moosejaw99]

at around 10 years old. I've been using it ever since, and don't plan on ever stopping.

Re:I learned how to use my slide rule...

[Dogtanian]

Well in answer to the question, no. I don't know what a slide rule is for.... but I know that one and one is two.

And if this one could be with you, what a wonderful world this would be.

Re:I learned how to use my slide rule...

[Urantian]

Actually, one AND one is ONE.

At least

[edittard]

At least a slide rule is more accurate than excel 2007.

Nuclear slide rule.

[pclminion]

I prefer to use a tactical nuclear slide rule, myself.

Re:Nuclear slide rule.

[jdray]

When I was in the Air Force (many years ago), I was a Loadmaster on C-130 cargo planes. Every aircraft had a sliderule as standard equipment, and we had to know how to use it to calculate load balances for the cargo, even though we used electronic calculators. The idea was that if our batteries died, we had to have a fallback. When the numbers you're dividing are seven digits for the numerator and four digits for the denominator, and your precision is 0.1, long division on a scrap of paper isn't reliable.

Of course

[Kozar_The_Malignant]

I did college physics, organic and physical chemistry with my trusty Pickett aluminum log-log slide rule. You needed one for real geek cred in those days.

Pheh, youngsters.

[Blnky]

You youngsters and your simpleton slide rules. Try a real one that makes you use that noggin of yours. http://home.earthlink.net/~apendragn/runish/sliderule/index.html

Around here

[Tarlus]

The only slide rule around here is to not push the kid in front of you.

Um No.

[VonSkippy]

I also don't know how to use a Flintlock rifle, trap/clean/spit roast a hare, catch a fish with my bare hands, hitch a wagon to a horse, or build/make/use a butter churn.

Since I live in the 21st century, I don't really lose sleep over those things.

Re:Um No.

[rubycodez]

actually, ignorant people in survival situations make all kinds of bad decisions and don't know how to treat or stabilize someone with injury. knowing poisonous from edible plants, cleaning properly cooking an animal without contaminating it, these are all things that people knew in that recent past but you'd better learn now rather than by trial and error (you die or are maimed for life if you're wrong)

Re:Um No.

[hey!]

I also don't know how to use a Flintlock rifle, trap/clean/spit roast a hare, catch a fish with my bare hands, hitch a wagon to a horse, or build/make/use a butter churn.

If you were seriously interested in shooting, you'd find a flintlock pretty interesting; you'd have at least a rough idea of how to operate one, although it might take you a bit of time to use it expertly. You'd at least get some pleasure out of messing around with one, and maybe take some lessons back for shooting modern firearms. If you were seriously interested in cooking, you'd have a pretty good idea of how to clean, split and roast small game, or how to use a butter churn.

If you are seriously interested in math, you are bound to find the slide rule intriguing.

Aside from idle curiosity, it is also true that taking the difficulty out of processes is not always an unmixed blessing, especially in education.

My daughter just started middle school, and one of the key math skills she is being taught is "number sense". This topic basically amounts to cognitive strategies for looking at a set of calculations and determining if certain possible results are reasonable. What is interesting is that this hole in math education was left by the removal of the slide rule from the curriculum.

The brain is a curious and largely unreasonable thing; it obstinately refuses to work in ways that seem like it should, yet performs brilliantly in ways it seems impossible that it might. For example, when I was a student, I experimented with using a tape recorder instead of taking notes, on the theory I could play the lecture back during what otherwise was down time. Aside from the obvious deficiencies of only having audio, I was disappointed to discover that at least for me, listening over and over to information doesn't do anything for recall. On the other hand, I was delighted to find that if I wrote down information as I heard it, mainly concentrating on the speaker but letting my hands semi-automatically follow along, my recall was so improved I seldom needed to refer to the notes I was taking. Something about the process of completing the circuit from input to output caused the information to stick.

In many other instances, I have found that trivial manual effort has unexpected rewards. I recently wanted to review probability theory, and I found it helpful to work through even trivial problems that I could see how to solve right away. It wasn't enough to have the insight, doing the work improved my comprehension and retention.

The lessons in number sense given by the slide rule are largely of the same kind. You'd think you could do as well having a superior calculating tool that effortlessly gives you more precision than you need. All you need to do is ignore the superfluous digits. It may even work that way for you, but I suspect many people's brains won't acquire the same skills.

Re:Of course

[Daniel_Staal]

I've never had one required (courses tended to require graphing calculators by the time I got to them), but I found one in my grandpa's desk and learned to use it. Then I carried it with me to high school and gave it to anyone who asked to borrow my calculator.

nerd phallus

[netsavior]

the bigger the slide rule, the more accurate the calculation...

No, and what the hell is the index line?

[cliveholloway]

"The index line on scale C is always put over the number to be multiplied on scale D"

What's the point of explaining how it works if you don't explain what each of the terms used is?

Damn nerds...

Re:No, and what the hell is the index line?

[dereference]

I have nothing to do with that site, and as many others have mentioned there are far better virtual slide rules available, but I did learn long ago how one of these things operates, and the instructions in TFA are horrible even if you know what you're doing.

First, the term "index" has the old-school meaning of the number "1" and it appears at either end of the C scale. On the left side of C it means 1, and the right side it means 10, but there are no actual decimal points involved (you're on your own for order of magnitude with this device) so they're equivalent at either end. Also, for multiply and divide, you don't need that hairline slider that covers all the bars; that's only useful if you need to align two values on non-adjacent rules. Just slide the center bar (the one that holds scale C) back and forth.

The other important point to note is that you'll see numerals 1-9 between 1 and 2; those are just convenience markers for 1.1 through 1.9. That first (smaller) 2 you see, reading from left to right, is really 1.2 not 2.0.

So to multiply 6x2, we can go either direction, starting at 2 and multiplying by 6, or starting at 6 and multiplying by 2. To start at 2, slide the center part of the bar so that the right-hand "index" (1) of scale C is directly above the 2.0 on scale D. Now to "multiply" you don't do anything; you just read the result, which is found on scale D, directly under the 6 you wanted to multiply. Here you'll see 1.2 is directly under the 6.

Wait, though, we used the right-hand index, which is 10 not 1, so we need to multiply the result by 10. So 1.2 becomes 12 (which is why I said you have to do your own decimal point management). To start at 6 instead, slide the right-hand "index" (1) of scale C directly above the 6 on scale D; your answer will on D again, directly under the 2.0 of slide C. Again, we used the right-hand index of 10, not 1, so we multiply the 1.2 by 10 to get 12.

How did I know to use the right-hand index rather than the left-hand index? Well, if you slide the left-hand index of C all the way to 2.0 on D, you'll notice that the 6 you need to multiply is off the edge of the device--an overflow, if you will--so you must essentially work with 10 rather than 1 and move the decimal at the end.

With this extremely trivial example, you should be able to follow the rest of the terribly-written instructions FTFA for divide (although you can do significantly more with a slide rule than just multiply and divide).

Re:Of course

[mabhatter654]

but in reality, justifying precision more than 4 significant places is really difficult using proper scientific/engineering methods. For instance 4 decimal places in surveying takes you to an inch range even over a mile of distance with hand tools. Average slide rules can do 2-3 fancy ones can hit that last place.

Of course

[Brett Buck]

I use a slide rule DAILY. It's an extremely useful and (if you know what you are doing) both accurate and fast. For many engineering problems 3 or 4 sig. figs. is plenty enough. The advantages are well-known - the most important being the elimination of "false precision" that you can get with a mindless calculation with a 10-sig-fig calculator.

    They are also just good things to have around. A good slide rule (Aristo, Nestler, Faber-Castell, etc) is just such a fantastically well-made device that you really need to see it to appreciate. The precision is something you don't see these days. Even a lowly Pickett is nicely made.

      Brett

I have

[ajs318]

When my grandad died, he left his "old" slide rules to my dad and me. My dad kept the original wood and cellulose one from the 1940s; I got the plastic one from the 1960s / 70s.

I soon got the hang of using it (and it can be quicker than a calculator sometimes), but I knew the general principle from before anyway. The main thing you have to remember is the slide rule only ever gives you the mantissa; you have to work out the exponent yourself. This means you have to do a rough mental calculation. People often put too much trust in calculators. When I was filling in order forms by hand in a previous job, I never used a calculator -- and I never got called out on a wrong total.

Pilots know how to use slide rules.

[fiid]

The E6-B is a rotary slide rule that pilots use for calculating wind correction angles, time/speed/distance problems, conversion between units (i.e. weight of a certain number of gallons of fuel), and fuel consumption.

It's preferred over digital devices because they still work when the batteries go flat, they are easy to use with one hand, and some models are actually smaller.

http://en.wikipedia.org/wiki/E6B

I feel bad

[planckscale]

My dad gave me his when I was a teen and said that he had used it for many years in college and the aerospace industry (Hughes). He gave it to me as a memento, and although he didn't keep it stuffed in his ass in Vietnam, it did carry a pretty significant sentimental value. It's lost; and although I did try to use it on several occasions, I only go so far as multiplication. It was a nice ivory color and had a leather carrying case. That thing probably helped launch 20 communication satellites.

Mildot Master

[dazedNconfuzed]

Slide rules are still in active use by - of all people - snipers. The Mildot Master is a sliderule for determining distances and ballistics for long-range precision shooting when using a rifle scope fitted with a "mildot reticle".

Simple, low-tech, durable and cheap - specialized slide rules are still useful for particular applications where computers are expensive & fragile overkill.

Re:Of course

[rubycodez]

but with a slide rule you can see a range of answers around the result for varying the factors. that process is extremely slow on a digital calculator. plus a slide rule forces you to think of the proper magnitude of the answer, with calculator people trust without thinking and "missed decimal point" or just fat-finger error gets believed more readily.

Re:Of course

[Kadin2048]

A whole lot of engineers calculated a lot of transfer orbits (not just Earth-Mars) with slide rules. In some ways they can be a lot safer than using a calculator, since they don't give you a false sense of precision.

E.g., divide 52 by 7 on a calculator, and it will spit out 7.428571428571, a completely correct although ridiculous answer when dealing with real-world quantities, since it blows away the precision of the input numbers. Slide rules require you to constantly consider the number of decimal places that you want, and encourage you to only write down the correct number of digits (so you might do the same result and put down 7.4).

Personally, I think some of the best engineering ever accomplished by man has been conducted mostly by slide rules. I wouldn't go so far as to say that we've necessarily regressed since then -- computers are great, don't get me wrong -- but it's not right to simply write off slide rules. They had very distinct benefits and I think students would be well suited if they were kept around as a pedagogical tool.

For dumb Americans:

[morgan_greywolf]

'Gymnasium' is what they call 'high school' in some countries.

Re:Of course

[rrhal]

A slide rule gets you 3-4 digits faster than a calculator. You have to know how to use it.

I was in the last class in my high school that learned how to use a slide rule. I was in the first class in my college where owning a scientific calculator was required for entry.

As a freshman my Econ professor asked the class if anyone with a calculator would do a division for him. I was carrying an inexpensive plastic slide rule in my back pack. I did the division and said the answer. As he turned to thank me he did a double take and said "What is this?" taking the slide rule from me and holding it up. I said "Its new, a solar powered calculator that never needs batteries." "What will they think of next?" he pretended to marvel.

The point of that whole story is that about 15 people probably had pulled out a calculator and started to do the division and I was able to beat all of them by several seconds.

Re:Of course

[lgw]

well, let's just say that you wouldn't want to have to calculate an Earth-Mars transfer orbit with a slide rule Why not - the Earth-Moon transfer orbits were calculated with slide rules originally. I didn't see any Lunar orbiters smack into the moon in the 60s! History proves that slide rules are better for astrogation.

Re:Of course

[dbc]

At the university I attended, freshmen engineering in 1973-74 required the use of a slide rule. In the 74-75 year, you could take freshmen engineering with either a "slip-stick" or a calculator. My freshmen year, fall of '75, required a pocket calculator. I was facile with a slide from from high school chemistry and physics, and can still do the basics, but haven't used one since. So the transition from slide rule to calculator was very fast.

A slide rule enforces estimating a reasonable answer before hand, and encourges arranging computations for economy of calculation. I think there is a big benefit to critical thinking skills in praticing basic computation with a slide rule.

That said, computers have made it possible to do what was formerly impossible due to computational expense. Integrated circuits would not be where they are if you couldn't burn many flops running spice. Cars would weigh more and get less gas mileage without mechanical simulations because they would have to be over-built in order to simplify strength calculations. Pre-computer-simulation camera optics suck when compared to modern computer optimized lens, ditto for antennas.

I once met a guy whose mother was a computer.... that was her job title: "computer". She worked for a university research department, where row upon row of "computers", mostly women, sat in front of mechanical calculators all day long, 40 hours per week, cranking through tablets of computations for various numerical models. Modern electronic computers enable solutions to problems there were too expensive to attack before, and life *is* better as a result.