The HP-01, code-named “Cricket,” was not a successful product for HP. It was too bulky and heavy, and HP sold it though upscale jewelry stores. But miniaturizing the math functions was quite an engineering feat, and when HP discontinued manufacturing the HP-01, its inner workings were destroyed so no one would copy the extraordinarily small package engineering. The HP Archives has a few of the remaining elements.
The HP-01 “calculator watch” performed more than three dozen functions to manipulate and interrelate time, calendar and numeric data. The user operated the 28 tiny keys with a stylus built into the bracelet. The HP-01 wrist instrument looked like a digital watch but was smarter than many pocket calculators. It performed more than three dozen functions to manipulate and interrelate time, calendar and numeric data. With six interactive functions (time, alarm, timer / stopwatch, date / calendar, calculator and memory) the HP-01 had 28 tiny keys that the user operated with a stylus built into the bracelet.