This two tariff watt hour meter was made by the General Electric Company in the UK. From what I understand, the Normal or bottom register is for the monitoring of power usage during the day and the Low or upper register is for power usage during night time hours. A small solenoid contained within the meter is connected to a timing device outside the meter, activating the solenoid at preset times. Seems a little unnecessary I may say, but seems to be a popular thing in the UK. 240 volt, 80 amp, 50 Hz. Works very well.