The slide rule began to go extinct in 1972 when its planet was shattered by an immense asteroid in the form of the digital calculator. I was there when it struck.

At only one order of magnitude greater expense, the Hewlett-Packard HP 35 increased the accuracy you could hold in your hand by some seven orders of magnitude. With the slide rule you had to figure out, in your head, where to put the decimal: is the answer 35,000,000, 3.5, or 0.000035? The slide rule didn’t say, it just gave you the "35". Suddenly, we had ten significant digits with the decimal point automatically in the right place, as HP proudly advertised. Now we take it for granted.

The day the HP 35 came out, I owned three slide rules. One of them was a very fine and complex one of elegant bamboo laminations with bright celluloid scales. I promptly sold it at a very good price to a blowhard who bragged that he’d always be able to outperform a calculator. "A quick motion of the slide will always be faster than punching in a pile of numbers," he told me. I couldn’t yet afford the calculator, but I could read the seven-segment numbers on the wall.

I also sold the large, circular slide rule that sometimes provided an extra decimal place over the slipstick, and which had given me a slight edge on tests and homework. The professor who bought it felt that calculators would always be too expensive and, as he pointed out, the slide rule had no batteries to wear out and would last for generations. Future generations, I thought, would have as little use for it as I would.

Beginning in my high-school days, it had taken hours of practice to become proficient at using the centuries-old invention. Carrying a full-fledged model with its log-log and trigonometric scales marked you as an ultrageek in high school. Now, it takes the latest titanium-cased portable supercomputer to get the same cachet. For nostalgia’s sake, I kept the last, and least, of my slide rules.

A few months after the HP calculator became available, I scraped together the money and purchased one. With a once-ubiquitous Dymo labeler (the kind that punches raised white letters in a colored plastic strip) I made a label for my remaining slide rule that said "OBSOLETE", stuck it on the slide rule’s leather case, and mounted the relic on the wall of my office. In what seemed a matter of days, you couldn’t find (or sell) a slide rule. I had gotten out just in time.

On my desk today, alongside my computer, is a $12.95 calculator. Solar-cell-powered, it needs no batteries, and while it won’t last for generations, it is somewhat more powerful and easier to learn and use than that original $400 HP 35. The calculators that my 21st century children use are programmable wonders that can, in microseconds, plot curves that used to take me hours to figure out, point-by-point, with my slide rule. The amount of mathematical intuition they get from these tools is wonderful, and having one is required in their high schools, there is no geekness attached.

The old HP 35, in its real leather case, sits on my bookshelf with its charger and well-written manual (though its batteries have long since lost their ability to be recharged), and on the wall of my office hangs my old slide rule, still functional, but equally useless...