## SLIDE-RULE WATCH (Feb, 1959)

SLIDE-RULE WATCHNEWEST gadget in do-every-thing watches is the Chronomat, a combination wrist watch, stop watch, timer and circular slide rule. With Swiss-made precision, the Chronomat gives you the time of day, let’s you time anything from an auto race to film souping, and provides a calculator that adds, multiplies, subtracts, figures percentages, ratios and even rates of money exchange. It’s scarcely larger than a 50-cent piece but there’s hardly a mathematical problem this gizmo can’t handle—except how many Brigitte Bardots can stand on the head of a pin. A dream of a gift, the Chronomat is sold by the Wakmann Watch Co. of New York City. The price? Only (gulp!) $110.

9:15 amHow many Brigitte Bardots can stand on the head of a pin? I’m guessing one…

10:24 ami use my cell phone for every one of the functions of that thing, and several more. i didn’t pay any $110 for it either. true, it only works when there’s a cell signal available — but that’s 99% of the time for me, and the remaining 1% i can do without any of its functionality anyway.

…um… what’s a film souping, and why would i want to time one?

10:25 amWith no linear scales, I don’t see how you could add on it, other than perhaps using some arcane manipulations using the clock face as a linear scale.

10:30 amSeveral companies still make watches with circular slide rules today. Often, they use the term “E6B”, from the name of a circular slide rule model that’s been popular with pilots for decades. Do a web search of that term along with “watch” if you’re interested. They’re often marketed as “pilot watches”, and some of them have lots of features like multiple time zones, analog/digital displays, etc. I had one for several years, and enjoyed it until one of its buttons broke and I couldn’t set it any more. The circular slide rule is handy for solving any ratio-type problem, like calculating a car’s gas mileage, converting between currencies, calculating tips, etc. I couldn’t get many significant digits of precision with a watch-sized slide rule, but it sure was handy.

10:48 amFilm souping, after some quick Googling, refers to developing film in a darkroom (by immersing it in the various processing baths).

You can, of course, get inexpensive digital calculator wristwatches these days which have all the same basic functionality and greater numerical precision in calculation, but far less panache.

10:52 am@Nomen: “Film souping” is a slang term for “film developing”. The time spent in the developer influences the contrast and density of the negatives. Film is developed in a light-proof tank, and since film is light-sensitive, you can’t open the tank up and take a peek to check the progress. So it’s important to time it accurately in order to get consistent and repeatable results.

11:20 amOne can add on such a device, sort of…

Let’s say one wants to add 5.7 to 3.9. Of course it’s much simpler to do it by hand, but you could divide 3.9 by 5.7 to get 0.6842… . Then, one can stick a 1 on the front without adding – and get 1.6842… . Multiply that by 5.7, and you have your answer, 9.6 .

Not really worth the trouble, I admit.

12:50 pmI had a cheap version of one of those back in the day before electronic calculators.

1:24 pmah, thanks Richard and Drew. next time i develop any film i’ll definitely time the process on my handy cell phone — but i doubt that’ll be any time soon; not much longer now before we’ll have to make our own film stock from scratch if we want to take pictures that aren’t digital captures.

2:03 pmCitizen still sells watches that are a bit like this. I’ve never genuinely used the slide rule on mine to do anything but show off, but it sure looks cool. And they’re a lot more than $110 these days:

http://www.amazon.com/C…