HP-01

The HP-01 was a marvel of miniaturization and intelligent design. It was HP's first watch and their first small algebraic calculator but it was more than just a wristwatch and a calculator in the same package. It combined them to do things that neither could do alone. Its user interface combined the best of both worlds. For example, to change time zones, the user displayed the time, added or subtracted the appropriate amount and stored the result.