Electronic watt-hour meter

Claim 1

An electronic watt-hour meter comprising: an electric power measuring device; a data setting device for setting data including time zone data and holiday data, and for setting programs for displaying measurement results with respect to different time zones in the form of effective, reactive, or apparent electric power as desired by using said data setting device; a data transmission circuit to which the data setting device is connected detachably; a programmable read only memory circuit (PROM) which receives the data and programs set by the data setting device through the data transmission circuit and stores the set data and programs; a read only memory (ROM) which preliminarily stores transmission programs for controlling said data transmission circuit; a central processing unit (CPU) which controls the power measuring device so as to receive measurement results therefrom in accordance with the set data and programs stored in said PROM, and which also controls receiving and storing data and programs in said PROM in accordance with said transmission programs in said ROM; a display device which displays the measured results under the control of said CPU; and a switch means for making said CPU operate in accordance with the data and programs in said PROM when said data setting device is detached from said data transmission circuit, and for making said CPU operate in accordance with the transmission programs in said ROM when said data setting device is attached to said data transmission circuit.