Users of one of the most successful gadgets of all time are celebrating its 30th birthday today. While technology gadgets have changed dramatically over the last 30 years, the HP 12c calculator has been unchanged since 1981.

Even after HP tried to introduce more-advanced devices and there are iPhone applications which mimic the calculator's functions, the 12c is common on Wall Street financial analysts desks. The 12c, which costs $70, is more than three times the cost of a standard calculator and yet has managed to be H-P's best-selling calculator of all time. The competition is the Texas Instruments' $28 BA II Plus.

The calculator runs on an operating system called "Reverse Polish Notation" it does not have  brackets or equal signs which makes long calculations run more efficiently. Once it is mastered, financial wizards do not want to have to learn something else so the calculator has remained, particularly among the older accountants. The calculator was lean on power and tough enough to be dropped on concrete.  Users did not want it changed at all.

According to the Wall Street Journal, users have objected to changes that made the calculator faster, and HP's only major facelift of the calculator was the 2003 launch of the pricier 12c Platinum, which has more memory and additional functions.