Technology History | 1501 Page Mill Road — The Calculator Was Named After Counting Its Own Keys

It has thirty-five keys, and that is the whole story of the name. Hewlett-Packard announced the HP-35 on 4 January 1972 at a press conference in New York, and the machine had been developed here, in the laboratories at 1501 Page Mill Road. What it replaced was the slide rule. Pocket calculators already existed in 1972 and they added, subtracted, multiplied and divided. The HP-35 was the first pocket-sized machine that also did logarithms and trigonometry, which is the qualifier that matters. Bill Hewlett had asked for something specific: a shirt-pocket version of the HP-9100, the desktop scientific calculator HP already sold. HP's own market research came back discouraging, with forecasts an order of magnitude below what the product went on to do. Hewlett overruled it, and orders in the first months ran past what the study had projected for the entire market. The price was $395, roughly twenty times a good slide rule. It weighed nine ounces and used reverse Polish notation, so there was no equals key and no brackets. Sales passed 300,000 units in the first three years. The HP-35 and the calculators descended from it went on to sell more than twenty million, making them the best-selling products the company ever had. Slide rules did not survive the decade as working instruments. HP moved to this address in the 1950s as an early tenant of the Stanford Industrial Park, the university-owned research campus that became the template for science parks everywhere. This is a working corporate campus and not open to the public. The IEEE recognised the HP-35 with a Milestone in electrical engineering, and the plaque is held at HP Labs here rather than anywhere a visitor can reach it. The cover photograph shows an HP-35 with its LED display lit. Photo: Holger Weihe, CC BY-SA 3.0, via Wikimedia Commons.