1. Apparatus for entering program data for a programmable resistance welding machine, said apparatus having control means operatively connected to said machine for controlling the operation of the machine, said control means including a computer means having a memory for storing said program data, said apparatus comprising (a) a numerical data entry keyboard consisting of a shift key for producing a first signal for designating selection of an item of program data to be entered, an incrementing key for producing a second signal for incrementing the numerical value of an item of program data, and a decrementing key for producing a third signal for decrementing the numerical value of an item of program data said apparatus having no other numerical data entry keyboards; (b) said computer means comprising a microprocessor connected with said keyboard to receive said first, second and third signals, to sequentially designate each item of program data in said memory in response to said first signal, and to set a numerical value for each item of program data designated on the basis of said second and third signals; and (c) a display unit connected to said keyboard and said computer means for displaying the numerical values of each item of program data.