Famously endorsed by Sting a kajillion years ago, the J-100 is a pretty special watch.
In a lot of ways it was an odd decision by Casio to put a calculator function into a sports/running watch. Watches, on the wrists of runners, have to deal with a lot of sweat so to have 20 buttons means there are 20 ways moisture could get into the delicate circuitboard. These early calculator watches were a reasonable size too, so added extra weight to the wrist that could quickly become annoying to a runner who is already tired.
And I’m yet to meet a runner who wants to perform calculations while they are in the middle of a jog.
Many Casio watches, particularly those sold from Asian countries have moderate to severe corrosion on the backside where sweat has seeped through the plated coating and pitted the case. Making the J-100 in resin only, with a SS back, alleviated that problem so Casio obviously had that in mind. Also, the plastic, or plated buttons were replaced on the J-100 with anodised aluminium (in orange, red or black, depending on the model you bought).
And, practicalities aside, the J-100 Pace Runner is loaded with features.
It has all the standard stuff, time, date, alarm, stopwatch and calculator, but it’s the pacer features where the J-100 really comes into its own.
Once you set your stride length, the watch can calculate elapsed time, distance covered, number of strides, length of stride and speed — all very important to the runner attempting, for example, a four-minute mile.
Casio predicted selling five million of these watches in the US alone and was even featured in a Sports Illustrated article at the time. (Update, this article no longer exists on the Sports Illustrated website so the link is to the article in The Wayback Machine).
And, of course, Sting was a big fan which didn’t hurt 😉 (photo from www.pocketcalculatorshow.com).