To determine the number of kilowatthours consumed both above and below the temperature at which a dual-energy heating system changes its heating source, you first need to read the data on your meter. If you have an electronic meter, the letters LHT (haut tarif / highest rate) are displayed to indicate the meter readings when the price is highest and the letters LBT (bas tarif / lowest rate) are displayed to indicate the readings when the temperature is equal to or higher than the threshold.
If you have an electromechanical meter, the dials with red needles indicate the meter readings at the high price whereas the dials with black needles indicate the meter readings when the temperature is above the threshold.
Subtract the meter readings indicated on your last bill for each period. To establish the ongoing consumption, multiply the result by 10 if you have an electromechanical meter.