Guest Post: Bring Back The Slide Rule!

The key point is that using a slide rule requires the user to keep track of the “order of magnitude” of the answers—because slide rules only give you four or so significant digits. This meant students of my generation when taking science and math courses were continuously exposed to order of magnitude calculations and you just couldn’t escape from having to make order of magnitude calculations all the time—students nowadays, not so much. Calculators have made skill at doing order of magnitude calculations (or Fermi calculations as they are often lovingly called) an add-on rather than a base line skill and that is a really bad thing.

Anyway, if you want to try a slide rule out, alas, good vintage slide rules have become collectible and so expensive— because baby boomers like me are buying the ones we couldn’t afford when we were in high school – but the nice thing is there are lots of sites like this one which show you how to make your own.

I am one of those baby boomers:

On the right are slide rules I actually used in school. Back in High School I had a 10″ slide rule which which is now long lost. I bought the circular slide (top right) back then as well, back then, being seduced by the alleged virtues of that design and the the wonders of the Edmund Scientific Co. catalog. Whatever those might be, the cheap cardboard construction led me to put it aside and return to the traditional design. Second on the right is the 6″ which got me through Carleton. When I arrived at Stanford in the fall of 1972 the first HP calculators were on the market. I had no hope of getting one of those wonderful machines but their advent caused the prices of traditional slide rules to nose-dive, allowing me to get the third example on the right, which got me through my M.S. in Applied Physics there. The three on the left I have acquired in subsequent years, at garage sales and similar events. I just could not let examples of such a beautiful technology end up in the landfill (Yes, I know: That way madness lies).

BTW, A quick look at eBay suggests the price problem quoted above might not be that bad.

But calculators really bug me in classrooms and, so I can’t resist pointing out one last flaw in their omnipresence: it makes students believe in the possibility of ridiculously high precision results in the real world. After all, nothing they are likely to encounter in their work (and certainly not in their lives) will ever need (or even have) 14 digits of accuracy and=2667″>Numbers and Precision gives examples of how Star Trek has contributed to the pro, more to the point, when you see a high precision result in the real world, it is likely to be totally bogus when examined under the hood.

Numbers and Precision gives examples of how Star Trek has contributed to the problem. I remember long ago watching Mr. Spock in one of those episodes and immediately thinking “He can’t possibly have that many significant figures.” I had a very good chemistry teacher my last year in high school (1967-1968), who made sure we understood all of this.

How does a slide rule work? See What can you do with a slide rule.