Page "HP-41C" Paragraph 2

Earlier calculators needed a key, or key combination, for every available function.

The HP-67 had three shift keys ; the competing Texas Instruments calculators had two (< u > 2nd </ u > and < u > INV </ u >) and close to 50 keys ( the TI-59 had 45 ).

Hewlett-Packard were constrained by their one byte only instruction format.

The more flexible storage format for programs in the TI-59 allowed combining more keys into one instruction.

The longest instruction required eleven keypresses, re-using the shift keys four times.

The TI-59 also made use of the < u > Op </ u > key, followed by two digits, to access another 40 different functions.

But the user had to remember the codes for them.

Clearly, a more convenient and flexible method of executing the calculator's instructions was in urgent need.

The HP-41C had a relatively small keyboard, and only one shift key, but provided hundreds of functions.

Every function that was not assigned to a key could be invoked through the < u > XEQ </ u > key ( pronounced EXEQTE — " execute ") and spelled out in full, e. g. < u > XEQ </ u > FACT for the factorial function.