Why the HP 12C still matters
The Hewlett-Packard 12C went on sale in September 1981 and is, astonishingly, still in production — the longest continuous run of any calculator model. Generations of bankers, appraisers, CFA candidates, and real-estate brokers learned finance on its keyboard. Its mystique comes from three things: RPN input that rewards fluency, a compact layout that puts time-value-of-money, cash-flow, and bond functions on the first row, and a metal bezel that survives being dropped onto a trading-floor concrete slab.
What this web clone covers
The calculator implements the arithmetic core, the 4-register stack (X, Y, Z, T) with automatic stack lift on ENTER, LSTx recall, twenty storage registers (STO 0-9 plus STO .0-.9), the full TVM solver for n / i / PV / PMT / FV using a bracketed Newton iteration on i, NPV and IRR on up to 80 cash-flow entries with grouped Nⱼ counts, amortization (interest, principal, and balance over a range of payments), 2-variable statistics (mean, sample standard deviation, n, Σx, Σy), and the usual percentage, roots, logs, and integer/fractional parts. BEG/END annuity modes and FIX decimal display work exactly as on hardware.
Reading HP 12C keystroke notation (f and g)
Before the example, a note on notation. The HP 12C has two shift keys — the yellow "f" and the blue "g" — that unlock the small gold and blue labels printed above and below each main key. Writing g END in a keystroke sequence means: press the blue g shift first, then press the key whose blue label reads END. On this clone (and on the hardware) that key is the digit 8; the key labelled BEG is the digit 7. Similarly, f AMORT means: press the yellow f shift, then the n key (whose yellow label reads AMORT). Once you learn the colour coding, the entire financial library fits on a 4-row keypad.
A quick worked example: mortgage payment
Imagine a 30-year mortgage for $300,000 at 6.50% annual interest. In HP 12C keystrokes:
30 ENTER 12 × n— 360 months into the n register6.5 ENTER 12 ÷ i— monthly rate into i300000 PV— principal (entered positive since the lender's view is an outflow to you; the HP 12C expects one of PV/PMT/FV to be negative)0 FV— loan is fully amortizedg END— press the blue g shift, then 8 (the key whose blue label reads END) to select end-of-month paymentsPMT→ returns −1,896.20 (your outflow per month)
Then 1 f AMORT (press 1, then the yellow f shift, then the n key whose yellow label reads AMORT) breaks down the first month into interest and principal. Continue the sequence to see every year of the loan.
About RPN
Reverse Polish Notation looks strange if you grew up on (3 + 4) × 5 =. In RPN you type operands first and then the operator: 3 ENTER 4 + 5 ×. Parentheses disappear, and your eyes stay on the stack instead of jumping back through an expression. Most HP 12C users report that after a few hours of practice they would rather not go back.