The Hewlett-Packard HP-01 was a calculator wristwatch. It was designed and manufactured by Hewlett-Packard. The HP-01 used 7 light-emitting diodes (LEDs)/digit in a 7 digit + decimal point arrangement for its digital display. Introduced in 1977 at the height of the LED watch craze, five models were available, two gold filled models and three stainless models. Prices were from $450 & $550 for the low end steel or gold to $850 (the equivalent of $2,500 to $3,300 in 2014 dollars). HP also sold a battery replacement kit that allowed the customers to change the batteries themselves. It used 2 batteries for the display and one for the processor IC. It also came with a ball-point pen with a stylus on the rear end. Most of the 28 buttons on the HP-01 were recessed and were designed to be depressed with a stylus that was stored by snapping it into the band. The production was stopped by the end of 1979.
The HP-01 was unique not only as the only Hewlett-Packard watch but due to these unique features:Datatype for time, date, and time interval, and the ability to perform mathematics on these datatypes.
A stopwatch that allows the stopwatch time to be multiplied or divided by a constant, and continuously display the results. This was referred to as a "Dynamic Rate Calculation." It could also tell you the day of the week for any day from 1900 to 2099.
The HP-01 was Hewlett-Packard's first algebraic calculator. Prior to the HP-01, all Hewlett-Packard calculators used Reverse Polish Notation (RPN). In later years, some HP calculators used a mixture of both.