The HP-12C is HP's longest and best-selling product, in continual production since its introduction in 1981. Due to its simple operation for key financial calculations, the calculator long ago became the de facto standard among financial professionals – for example, most investment banks issue HP-12Cs to the members of each incoming class of its investment banking analysts and associates. Its popularity has endured despite the fact that even a simple, but iterative, process such as amortizing the interest over the life of a loan—a calculation which modern spreadsheets can complete almost instantly—can take over a minute with the HP-12C. The 1977 October edition of the HP Journal contains an article by Roy Martin, the inventor of the simple method of operation used in HP financial calculators, which describes, in detail, the mathematics and functionality built by Prof William Kahan (from UC Berkeley) and Roy Martin that is still in use today.
Later HP financial calculators are many times as fast with more functions, but none has been as successful. The HP-12C's programming mode is very intuitive and works like a macro operation on a computer. Basically, the keys one would press in the calculating mode to arrive at a solution are entered in the programming mode along with logical operators (if, and, etc.) applicable to the solution. After the programming is complete, the macro will run in computation mode to save the user steps and improve accuracy. There are 99 lines of programmable memory on the HP-12C, and 400 lines on the HP-12C Platinum.
Over its lifespan, the processor's technology has been redesigned to integrate all the circuitry into a single chip and to refresh the manufacturing process (as the foundry could no longer manufacture the necessary chips, having moved on to making higher-density chips). However, HP's market research found in the late 1980s that the users did not trust results obtained too quickly and so the CPU speed was never improved from the original 200 or so kHz. In the late 1990s, the CPU was changed to a 3V process and the battery was changed to a single 3V cell.
In 2008, HP modified the design so that new production runs contain an ARM processor which runs an emulated version of previous chips. This has brought advanced possibilities such as flashing new firmware, not previously possible. HP also released a software development kit (SDK), making it possible to make new and custom operating systems. The calculator runs 20 times faster on most benchmark operations. This version is colloquially known as the HP-12C+ although HP does not market it as a different product. This is the version sold by TheCalculatorStore.com.
The HP-12C is one of only four calculators permissible in the Chartered Financial Analyst exams, the others being its sister, the HP-12C Platinum, and the Texas Instruments BA II Plus and BA II Plus Professional.