In praise of the slide rule

Slide rules: work under water, in sand, and are always on. Slide rules can be held and operated with the same hand, either hand. Slide rules don’t need batteries or solar for their cells; they can be used in bright sunlight. Slide rules can be dropped from a moving car and still work perfectly, don’t care if you throw them across the room and have an indestructible display. Slide rules round off automatically and give exactly the right number of decimals and never give you an error message. In six inches they give the ability to multiply and divide any number, take the square and cube roots, give the inverse of a number, give the log and ln, and basic trig functions. What’s not to like? Holding one in the hand is like holding mathematics. Everybody should own one.

My collection is shown in the photo. The top two rules  are starters for the young I suppose as they only multiply and divide. Third from the top is also a simple introductory rule of about the 1960s-era when aluminum was introduced. Fourth and fifth down are mostly the same, duplex models, with scales on both sides, the second rule being the reverse side of the first; as is obvious this is the one for the serious calculator. It was one of these I toted to my senior high school physics class. My teacher, Mr Eich, had a huge 6 foot long rule hanging over the blackboards. He could move the slide strip and cursor to demonstrate a calculation for all to see. Finally the last two are just compact shirt pocket versions of the big duplex ones, again the second being more or less the reverse side of the first. I still carry the bottom one, the last one I ever bought while in college in the late ‘60s, on trips and for quickly checking a calculation when reading; it’s just so much faster than key-stroking numbers into a digital calculator.

For some reason slide rule are considered devilishly hard to learn how to use. Or are totally misunderstood. For instance in the movie “Apollo 13” when a ground control engineer is told to add two numbers together and he furiously cranks it out on his slide rule, something, one of the only things, a slide rule can not do.

My friends, if you will simply take a slide rule in hand and play with it a few minutes you will discover how very easy they are to use. You will see the product of two numbers jump right out at you and division being the reverse of multiplication will happen just as easily. You can be a self-taught slide rule user with only a few minutes work. And soon you will realize the usefulness of the answers.

My point then is that the joys of holding and operating a slide rule are palpable and should not be missed.