Derived by averaging the watt second consumption over the past hour. Use an array of 60 words to store the average watt seconds consumed over the last minute then after you have a full hours worth of data in the 60 word array, average those values to get your Present KWH Consumption meter. Then every minute after that update the oldest value in the array, average again and update the meter. Value is 0 until the minimum 1 hour of data has been accumulated.