. " explanation of the mode of operation of the modification; FIG. 8 is a top view of a second embodiment of the present invention; FIG. 9 is a schematic block diagram of the second embodiment; FIG. 10 is a table showing the relationship between the key operations and the resulting displays; FIG. 11 is a block diagram of a modification of the second embodiment; FIG. 12 is a top view of a third embodi" . . .