The HP-41C had a relatively small keyboard, and only one shift key, but provided hundreds of functions. Clearly, a more convenient and flexible method of executing the calculator's instructions was needed. The TI-59 also made use of the Op key followed by two digits to access another 40 different functions, but the user had to remember the codes for them. The longest instruction required eleven keypresses, re-using the shift keys four times. The more flexible storage format for programs in the TI-59 allowed combining more keys into one instruction. Hewlett-Packard were constrained by their one byte only instruction format. The HP-67 had three shift keys (gold 'f', blue 'g' and black 'h' prefix keys) the competing Texas Instruments calculators had two ( 2nd and INV) and close to 50 keys (the TI-59 had 45). 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.Įarlier calculators needed a key, or key combination, for every available function. The alphanumeric LCD screen of the HP-41C revolutionized the way a pocket calculator could be used, providing user friendliness (for its time) and expandability (keyboard-unassigned functions could be spelled out alphabetically). The HP-41C's alphanumeric display allowed it to display numbers, characters, and symbols.

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