Calculator
A clean on-screen keypad calculator with full keyboard support and chain operations.
Keyboard: digits, + - * /, Enter = equals, Backspace = erase, Escape = clear
What is it
This is an immediate-execution calculator, just like the pocket one: pressing an operator acts on whatever is on the screen right away. Type 2 + 3 × 4 and you get (2+3)×4 = 25, because each operator runs the pending calculation before moving on. Two lines are shown: the expression on top, the current number or result below.
Notes & fun facts
Immediate execution is why old calculators felt quirky: people would type 2 + 3 × 4 expecting 14 (the math way) and get 25. Spreadsheets and phone calculators quietly switched to algebraic order decades ago, but the pocket-calculator way still lives on in plenty of cheap keypads.
Origin & history
Mechanical calculating machines go back to Blaise Pascal, who built his adding machine in 1642 at age 19 to help his father, a tax official. Gottfried Leibniz improved the design around 1673 so it could multiply too. The first electronic desktop calculator arrived in 1961 (the Bell Punch ANITA), and pocket-sized ones like the HP-35 (1972) turned arithmetic into something you carried in your shirt pocket.