|Same specifications as the HP41CV with the equivalent of an HP Extended Functions/Memory module & a Timer Module.|
Around the time of the HP-67, an article in the Hewlett-Packard Journal, stated that electronic technology was no longer the only limitation of pocket calculator progress. The human interface was becoming an even greater barrier to adding more functionality. The HP-67 was an excellent example of the problem. It had three shift keys and most of its other keys had four functions. HP was running out of keyboard space for new functions, and many users found it difficult write and use numeric-only programs.
The HP-41C overcame these limitations by adding alphanumeric capabilities to both the display and keyboard. The keyboard had an "Alpha" key that toggled the keyboard between alpha and the normal calculator mode. (The alpha characters were printed on the slanted faces of the keys.) If the user needed a function not printed on a key, the name of the function could be typed in and executed. (About half of the HP-41Cs functions were preassigned to keys.)
Because typing out the name of a function could be cumbersome, the HP-41C added another toggle key called "user". The user could assign any built-in function or user program to any key. Once the keyboard was placed in user mode, any assignments made by the user overrode the label on the key. (With the gold shift key, this allowed two user functions per key.) The user toggle state remained set even when the calculator was turned off allowing true keyboard customization.
To make it easy to remember keyboard assignments, HP provided keyboard overlays along with preprinted labels for all built-in functions and blank labels for user functions. In addition, whenever a key was held down, its function name was displayed. If it was the wrong key, the user could continue to hold it until the display showed "NULL" when meant the function was canceled.
Of course, HP didn't just improve the human interface. The HP-41C had more memory (now non-volatile) than its predecessor, more functions, improved programming, and could be expanded with both RAM and ROM modules.