Interview with David Cochran on creating the HP35 calculator

This is the 1st in a series of interviews of individuals and teams who have created what I would consider killer innovations. In this episode, I recorded an interview with David Cochran, the original Product Manager of the HP35 calculator.  Per the entry in Wikipedia:

HP35 Calculator

The HP-35 was Hewlett-Packard‘s first pocket calculator and the world’s first scientific pocket calculator (a calculator with trigonometric and exponential functions). Like some of HP’s desktop calculators it used reverse Polish notation. Introduced at US$395, the HP-35 was available from 1972 to 1975.

Market studies at the time had shown no market for pocket sized calculators. In about 1970, HP co-founder Bill Hewlett challenged his co-workers to create a “shirt-pocket sized HP-9100“. Thus, the first ~12 HP-35 portable calculators were made as a “hack” by and for other engineers at HP. It is rumored that the development engineer got carried away and implemented a full suite of scientific functions to satisfy requests from his co-workers. When these prototypes proved popular, HP decided to turn the HP-35 into a commercial product. The HP-35 was the first calculator with a full suite of trigonometric and transcendental functions.

In the first months, orders were exceeding HP’s expectations as to the entire market size, which was 10,000 units per year. Before the HP-35, the only practical portable devices for performing trigonometric and exponential functions were slide rules. Existing pocket calculators at the time were only four-function, i.e., they could only do addition, subtraction, multiplication, and division.


In this interview, David not only shares the history and how of creating the HP35, but also shares stories about Bill Hewlett, David Packard and others including Steve Wazniak.

You can download the podcast here.

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