Buying guides
Read one of these before you buy. They cover which HP 12C to get, telling an original 15C from its reissues, the HP-41 line and its modules, learning RPN, and checking any old calculator from the listing photos to the first keystroke. New to old calculators? Start with the condition checklist.
Which HP 12C to buy: the original, the Platinum and the special editions
Every HP 12C you'll find used, from the 1981 original to the Platinum, the 25th Anniversary, the Prestige and the 30th Anniversary, and which to buy.
Read the guide →HP-15C original vs Limited Edition vs Collector's Edition: how to tell them apart
How to tell a 1982 HP-15C from the 2011 Limited Edition and the 2023 Collector's Edition: batteries, labels, the MEM test, the LE's bugs and clones.
Read the guide →HP-41C, 41CV or 41CX: memory, modules and which one to buy
The three HP-41 models explained: memory, what's built in, the ports and modules, the separate card reader, how to tell them apart and what to check.
Read the guide →RPN in one hour: how to use an HP calculator
Learn RPN on an HP in an hour: ENTER, the four-level stack, chained sums, LAST X, percent and a 12C loan payment, plus which calculators to learn on.
Read the guide →How to check a used HP or TI calculator
Leaked batteries, dead packs, chargers, displays, keys, self-tests, card readers, memory, serial numbers and clones: how to check a used HP or TI calculator.
Read the guide →