The alphanumeric LCD screen of the HP-41C revolutionized the way a calculator could be used, providing user friendliness (for its time) and expandability (keyboard-unassigned functions could be spelled out alphabetically). By using an alphanumeric display, the calculator could tell the user what was going on: it could display meaningful error messages (ZERO DIVIDE) instead of simply a blinking zero; it could also specifically prompt the user for arguments (ENTER RADIUS) instead of just displaying a question mark.