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...

[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.

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: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

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

[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.

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.