a hand - held , programmable , electronic calculator is capable of performing a larger number of functions than the number of keys on its keyboard and has one or more prefix keys to allow one function key to initiate more than one function . each key generates a unique key code when it is depressed , and the calculator may be programmed by storing a series of the key codes in a memory . memory space can be saved by generating unique merged codes to represent the combination of a prefix key and a function key , and storing this single merged code rather than the two key codes .