Slide rule article in today's Wall Street Journal

From: Tony Duell <>
Date: Tue Feb 18 13:50:00 2003

> Hi listmates, some might be interested in this:
> - Evan K.
> =========================
> Calculating Collector Scours Globe Hunting for Slide
> Rules

> Slide rules, which resemble either rulers or discs,

There are also the cylindrical type, with helical scales. Normally they
only have the the equivalent of the C and D scales (simple logarithmic
scales) so can only be used for mulitiplication and division, but those
scales are pretty long as a resuit of them being wrapped round the cylinder.

> were a boon to the mathematically minded and a bane to
> everyone else. To multiply two times two, for example,
> the user moves the "zero" of one scale to the number
> two on another scale. Then the user looks at the
> number two on the first scale, and above that is the
> number four.
> Confused? So were many other people, which is why the

I am confused too. I am very confused by a 'zero' on a logarithmic scale!

> slide-rule industry took a big hit in 1972, when
> Hewlett-Packard Co. launched its first scientific
> hand-held calculator. Almost overnight, demand for

The HP35. An amazing little machine for the time. And it's suprising how
many of those are still working 30 years later!


> But slide rules are more than quirky bric-a-brac to
> the true believers. Many engineers still swear by
> them. Some teachers today are reintroducing the
> devices into classrooms, arguing that they foster
> more-complex thought processes than electronic
> calculators do. At the University of California in San

One advantage of the slide rule is that it only gives the mantissa. You
have to calculate the exponent -- the order of magnitude -- separately.
It therefore encourages you to develop the skill of doing order of
magnitude calculations in your head, something that is not hard to do,
and which prevents silly mistakes. I've lost count of the number of times
I've been given answers which are rediculously wrong (things like needing
a 2.5 GOhm resistor for an LED limiter, or that the wavelength of the
dominant line in sodium light was 5 metres).

As an aside, I was once teaching a student how to calculate the resistor
values he needed. The problem simplified to a potential divider, and I
asked him for a calculator. Intending to confuse me, he handed me a slide
rule (Hint : I know what most calculating devices are, and how to use
them). I pointed out this was the ideal thing. I set the ratio of the 2
resistors on the C and D scales, and looked along for places where
prefered values lined up.
Received on Tue Feb 18 2003 - 13:50:00 GMT

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