Dalai(‘s) Rules!!

About 10 years ago, I went through a phase of collecting slide-rules, among other weird scientific things. My collection languished in my office at the hospital for quite a while, then moved home when the hospital needed the space. They gathered more dust until a few weeks ago when Mrs. Dalai decided that the house (the WHOLE house) needed cleaning. She found the rules above stacked in a corner, and said, “Why don’t we put these on the wall?” Which I did, after shoveling out several years of accumulated trash, I mean stored items, in the home office.

Slide rules were once an absolute necessity amongst the engineering, math, and other intellectual folk. (I won’t even try to tell you much about their design and function, but the Wikipedia article on the subject is excellent. And here is a great introduction into the actual use of slide rules.) Slide rules rode to the moon to augment the primitive on-board computers. (Buzz Aldrin’s moon-flown rule sold at auction for $77,675 in 2007.) But then along came the electronic calculators, especially the Hewlett-Packard HP-35, and the slide-rule soon went the way of buggy-whips.

Well, not completely. Some of us still remember what they are, and maybe how to use them. I had a 1 week elective in the use of this archaic technology whilst in junior high in the 1970’s, and a love for the elegance of the devices stuck with me. There were still stores selling slide-rules at that time, and a few of my high-school friends actually still used them into the mid-70’s. My parents wouldn’t let my buy one, however, rightly seeing the way things were going.

Slide rule collecting today has a limited but enthusiastic following. Some of the little buggers (the rules, not the collectors) have become quite valuable, and my old investment has done rather better than many of my stocks!

For a time, my mania led me to buy quite a few varied rules. I ultimately concentrated on the large school-demonstration rules, that are now on my office wall above. My pride and joy is the third from the top, a six-foot version of the Keuffel & Esser Decilon 10. As it turns out, there are quite a few different versions of the gigantic classroom rule, as catalogued in this page from the Slide Rule Museum (yes, there is one), although my Decilon did rate a large entry:

These things are rare enough these days that mine is probably one of those pictured above!

I also concentrated on the even more unusual clear versions that were used with the old overhead projectors, such as this Aristo (image from Rod Lovett’s Slide Rules):

There is actually a Keuffel & Esser Deci-Lon projection version, Model 68-1955, and if you happen to have one, we need to talk!

The final piece of the collection is a totally in software, the Slide Rule App for the iPhone:


The mechanical versions work better, I’m afraid, but it’s interesting to see how technology converges.

Thanks to the internet, and especially eBay, it is possible to connect collectors, buyers, and sellers of this old but still facinating technology. Slide rules rule!

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