1. A programmable calculator having a program mode and a run mode comprising: input means having keys for generating keycodes corresponding to numeric data and instruction legends denoting operations to be performed by the calculator; a first memory unit coupled to the input means for storing generated keycodes; a second memory unit having stored microinstructions and being coupled to the input means; a computing unit coupled to the input means and the first and second memory units for performing operations employing microinstructions stored in the second memory unit in response to keycodes from the input means and the first memory unit when the calculator is in the run mode and for storing keycodes from the input means at data locations corresponding to program line numbers in the first memory unit when the calculator is in the program mode and being responsive to the calculator being turned on for storing selected information at all locations corresponding to program line numbers in the first memory unit; and output display means coupled to the computing unit for displaying the results of operations performed by the calculator when the calculator is in the run mode and for displaying a key code corresponding to an actuated key and a number corresponding to a program line number when the calculator is in the program mode.