Here is a photo Robert Miles and James Alleman, formerly of Purdue University, holding a giant slide rule.

"A what?" You say. Hmmmm you're not quite the geek you thought you were. Well not a particularly old one anyway. For 300 years the sliderule was the basic tool of the mathematician, the engineer and the physicist. It was the key calculating device for the sciences until the release of Hewlett Packard's HP35 scientific calculator in the 1970s.

The Green Man remembers buying his last slide rule, discussing with the salesman how it was so sophisticated it would last his scientific career. Little did he know that its position in the scientific community would be usurped within a year or so by the HP35. As Robert Miles reminises

Many people who push the buttons on calculators don’t really know what the numbers mean, while on a slide rule you had to analyze where the decimal point went, and you had to better understand the mathematics

It is elitist I know, but it was a good feeling being in control, to have a sufficiently attuned sense of the beauty of numbers and how they worked to be able to fully utilise this magical device.

Of course the HP35 calculator did not relinquish this domain to the uneducated masses either. Using "reverse polish notation" for its arithmetic, it was completely unuseable by anyone other than mathematicians. (For those of you who have not been shown the secret handshake, reverse polish notation places the operator at the end of the operation not in the middle where it normally is. For example to add one and two together on a normal calculator you would do "1" "+" "2" "=". In reverse polish notation you would do "1" "Enter" "2" "+")

Ah, enough reminising, you can do more yourself by visiting the Purdue University website where there is an article on Purdue's museum of sliderules.