Plugger challenge


Here's a challenge for all those that have identified themselves as pluggers...

At a recent HPCC meeting in London, Hugh Steers came up with two common calculations that are simpler to perform on a sliderule than on a modern calculator. Before I reveal them, what can you come up with?


"Simpler" would depend on the calculator, but I find it easier to do R -> P and P -> R calculations on a slide rule than on most calculators.


Try a number raised to the 2/3 power. Set the cursor on the number on the K scale and read the result on the A scale. And, of course, do the opposite to raise a number to the 3/2 power.

A slide rule such as the K&E Log Log Duplex Decitrig that I used in college has additional scales folded at pi. So to multiply a number by pi simply set the cursor at the number on the D scale and read the result on the DF scale. Do the opposite to divide by pi.

On some of the simpler Mannheims which do not have an ST scale the S scale works with the A and B scales, e.g., a Sterling Precision. Align ends of the scales on the slide with the ends of the scales on the frame. To find the square root of the sine of an angle set the cursor on the angle and read the result on the D scale. And, of course, to find the 3/2 power of the sine of an angle ...

I can go on and on, but I'll stop there for now.

Edited: 5 Nov 2009, 9:38 p.m.


Starting at the grass roots, any set of proportions is easily and completely read on a slide rule, while it takes you repeated calculations with a calculator.


Walter scooped me!

My fuel flow versus time is a simple ratio. Once set on the C and D scale (or folded scales) all you do is move the cursor.

Same with money exchange rates. Set the rate and move the cursor only for each subsequent conversion.

It's just that easy.

Cheers, Geoff

Off to Sydney, Australia from Vancouver, British Columbia, Canada. Flight plan time 15 hours airborne non stop. Exchange rate is 85 cents Aussie to 1 Canadian. All set on my 1965 Breitling E6B slide rule watch!



Hi Geoff, wish you a happy landing d8-)


Thanks for the answers - some interesting ones there. As for Hugh's, one you got, the other is more debatable as to whether the calc is easier or not...

Here are Hugh's suggestions:

  1. comparators. if you want to figure out which washing powder is the best value and perform quantity/price * other-quantity, you only need to see if the slider moves greater or less than the start point and not the exact value.

  2. figuring out the bill in Indian restaurants. usually there is a prime number of diners and it's dark.assuming you're not carrying a LED calculator, it's difficult to read the screen in the dark. also, slide rules are good for rounding up to include the tip - you just go to the next significant mark after the divide. furthermore, the 1/x scale is good for this calculation also and a pocket rule is plenty accurate which fits neatly in a jacket pocket.


I love Hugh's input on the Indian restaurant. Thanks for the laugh, it has been one of those weeks (yes, week, even though it is Monday).


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