The HP-35 was Hewlett-Packard‘s first pocket calculator and the world’s first scientific pocket calculator:[1] a calculator with trigonometric and exponential functions. It was introduced in 1972.



In about 1970 HP co-founder Bill Hewlett challenged his co-workers to create a “shirt-pocket sized HP-9100“. At the time, slide rules were the only practical portable devices for performing trigonometric and exponential functions, as existing pocket calculators could only perform addition, subtraction, multiplication, and division. Introduced at $395 (equivalent to $2,414 in 2019),[2] like HP’s first scientific calculator, the desktop 9100A, it used Reverse Polish Notation (RPN) rather than what came to be called “algebraic” entry. The “35” in the calculator’s name came from the number of keys.

The original HP-35 was available from 1972 to 1975. In 2007 HP announced the release of the “retro”-look HP 35s to commemorate the 35th anniversary of the launch of the original HP-35.[3]

The HP-35 was named an IEEE Milestone in 2009.[4]