coded interchangeable key pad assemblies alternately installed on a keyboard so that one of a variety of programmable sets of keyboard functions is enabled for selection by user actuation of the keys . each key pad assembly has a durable construction and is securely attachable to the remainder of the keyboard . each key pad assembly is installed on the remainder of the keyboard and interacts with the system with which the keyboard interfaces , preferably a programmable system , to provide a custom key panel for the user so that key functions can be tailored to a desired selection of operations available to the user upon actuation of the keys .