HP-12C

The HP-12C is a pocket calculator laid out on its side, wider than it is tall, about thirteen centimetres by eight. A brushed gold band across the top holds a single-line display of ten digits and a small HP badge; below it sit thirty-nine black keys on a black face, each carrying a white label, with further functions printed in orange above and in blue below. There is no equals key. In its place is a tall ENTER key, for the calculator works in Reverse Polish Notation.

Hewlett-Packard introduced it in 1981, one of five matching programmable calculators it called the Voyager series. The 12C was the financial one, with keys for loan payments, interest rates, net present value, internal rate of return, bond yields and depreciation, and methods worked out by William Kahan and Roy Martin. Within eight years the other Voyagers had been discontinued. The 12C kept selling.

It became a fixture of finance. The Wall Street Journal, marking its thirtieth birthday, called it HP's best-selling calculator of all time and found analysts who had used the same one for twenty years; it remains one of four calculators allowed in the Chartered Financial Analyst examinations. Users have even objected to making it faster. When HP launched a more capable 12c Platinum in 2003, it kept the original on sale beside it.

What has changed is inside the case. The 12C has had at least nine hardware revisions: new chips, a single lithium coin cell instead of three button cells, and from 2008 a modern processor running the original software in emulation, so that it answers in a fraction of the old time. The keyboard and display have not changed. Since 2022 it has been made by HP's licensees under the HP name, with 'Hewlett-Packard' gone from the faceplate, and it costs about £55.