As Hewlett-Packard boasted at the time: "The HP-01 is a digital electronic wristwatch, a personal calculator, an alarm clock, a stopwatch, a timer, a 200 year calendar...and yet it is more than all of these."

It is actually the HP-01's ability to combine all its functions that makes this watch truly unique. It indeed allows you to integrate metrics such as time, speed and cost into your calculations, and perform the kind of computations NASA needed a dedicated room for in the late 1950s. For instance, you could find the required travel time to a specific point, or discover on which date a specific process would end. Add to that a very advanced calculator, and you were sure to never flake your math exam. Finally, you could use a recall function with associated data, much like an agenda; one ad specifically mentions an arranged call to your wife with the phone number then displayed on the screen – a reminder that cell phones were not around at that time so those logistics were slightly harder.

Not only that. If you are of a certain age you may remember something called Reverse Polish Notation. This was a way of entering numbers and operators that saved memory space but required some mental gymnastics as you would include operators after numbers. To get three plus four, for instance, "3 4 +" would be entered. It made for speedier calculations but was not intuitive, and this was the first calculator from Hewlett-Packard (wristwatch or otherwise) to use standard algebraic notation, rather than RPN.