Hugh Pickens writes "The Wall Street Journal reports that Hewlett Packard's HP-12C financial calculator has remained outwardly unchanged since its introduction in 1981. 'Once you learned it on the 12C, there was no need to change,' says David Carter, chief investment officer of New York wealth-management firm Lenox Advisors, who has owned his 12C for 22 years and still keeps it on his desk. 'It's not like the math was changing.' The 12C, which costs $70 on HP's website, is HP's best-selling calculator of all time, though the company won't reveal how many units it has sold over the years. The 12C still uses an unconventional mathematical notation called 'Reverse Polish Notation,' which eschews parentheses and equal signs in an effort to run long calculations more efficiently."