1. A calculator for processing digital operand signals, comprising: keyboard input means including a first set of keys for entering digital operand signals to be processed and further including a second set of keys for entering digital operator signals determining the manner in which the digital operand signals are to be processed; buffer storage register means, coupled to the keyboard input means, for temporarily storing digital operand signals entered by the keyboard input means; a plurality of data storage registers, coupled to the buffer storage register means, for storing digital operand signals transferred thereto from the buffer storage register means; processing means, coupled to the keyboard input means, the buffer storage register means and the data storage registers, for processing entered digital operand signals in accordance with entered digital operator signals, said processing means including first means for selectively transferring an entered digital operand signal between the buffer storage register means and one of the data storage registers in response to a digital operator signal entered by operation of a sequence of keys including one of the first set and one of the second set and designating one of the data storage registers, said processing means further including second means for selectively combining entered digital operand signals in accordance with other digital operator signals entered by selected keys of the second set to provide resultant digital signals; and output means, coupled to the buffer storage register means and the processing means, for providing an output indication of the resultant digital signals.