This completely new design measures the mains voltage and the appliance's load current, then multiplies the two (taking into account the power factor, including any phase difference) to work out the power being used. Then it integrates this over time to determine the total energy usage in kWh (kilowatt-hours). At the same time, it multiplies the power consumption by the energy tariff that is applicable at the time (ie, peak/off-peak) and keeps a running total of the energy cost over time.
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