The monthly reading of our customer meters varies from time to time due to holidays or bad weather. In Tongatapu, it can be up to 25 days to manually read over 15,000 meters while generators meters are read within minutes at the last day of every month. Because of this, a 12 month moving average is used to adjust for the anomalies. This monthly reading of meters determines TPL total monthly generated power, generation parasitic losses, power sent out to customers and power consumed by customers. TPL line losses are then determined by subtracting the power consumed by customers from power sent out to customers.