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# Interview with David Cochran on creating the HP35 calculator
- URL: https://www.philmckinney.com/interview-with-david-cochran-on-creating-the-hp35-calculator/
- Published: 2009-06-20T22:17:38.000Z
- Updated: 2026-04-01T14:10:12.000Z
- Author: Phil McKinney
- Tags: Past Shows, Studio Sessions, David Cochran, HP35, #wp, #wp-post, #Import 2026-03-26 05:08

Download [KI\_20090620.mp3](http://libsyn.com/media/philmckinney/KI%5F20090620.mp3?ref=philmckinney.com)

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](http://en.wikipedia.org/wiki/HP-35?ref=philmckinney.com):

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*The HP-35 was [Hewlett-Packard](http://en.wikipedia.org/wiki/Hewlett-Packard?ref=philmckinney.com)‘s first [pocket calculator](http://en.wikipedia.org/wiki/Pocket%5Fcalculator?ref=philmckinney.com) and the world’s first scientific pocket calculator (a calculator with [trigonometric](http://en.wikipedia.org/wiki/Trigonometric%5Ffunctions?ref=philmckinney.com) and [exponential functions](http://en.wikipedia.org/wiki/Exponential%5Ffunction?ref=philmckinney.com)). Like some of HP’s desktop calculators it used [reverse Polish notation](http://en.wikipedia.org/wiki/Reverse%5FPolish%5Fnotation?ref=philmckinney.com). 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](http://en.wikipedia.org/wiki/William%5FHewlett?ref=philmckinney.com) challenged his co-workers to create a “shirt-pocket sized [HP-9100](http://en.wikipedia.org/wiki/HP-9100?ref=philmckinney.com)“. 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](http://en.wikipedia.org/wiki/Slide%5Frule?ref=philmckinney.com). Existing pocket calculators at the time were only four-function, i.e., they could only do addition, subtraction, multiplication, and division.*

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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](http://libsyn.com/media/philmckinney/KI%5F20090620.mp3?ref=philmckinney.com).