Abacus HP-35, c. 1972
Introduced in 1972, the HP-35 handheld scientific calculator had been an enormous success for HP, selling 300,000 units in the roughly three and one-half years it was on the market. Bill Hewlett had stood behind the HP-35 and pushed for its development even when the results of market research initially indicated that sales would be disappointing. As a joke, a group of employees gave Bill this abacus disguised as an HP-35 electronic calculator.
In 1992, on the occasion of the 20th anniversary of the HP-35, Bill donated his abacus HP-35 to the HP Archives.