5. The Cricket (1978)

HP 01 Introduced on July 1, 1978, but announced on June 1977, it was a one-of-a-kind HP calculator, as it combined calculator and watch functions. One unusual aspect of this watch was that the current date or time could be included in the calculations. It included a stylus on the wrist band that could be pulled to press the recessed buttons and perform calculations. The watch functions on the other hand were accessible through raised keys to allow for easy (non-stylus) access. It was released in Steel or Gold with matching bands, as well as leather ones, and sold through expensive watch stores, rather than usual calculator dealers. Due to its uniqueness, I have included multiple pictures of this unusual and rare HP calculator. Code name: Cricket. Original price: $650 (steel), $750 (gold)

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Click on the for a picture of the manual's front cover.