Demand meters measure volt-amperes (in kVA), that merge both reactive (reflected) and actual (consumed) power. In its easiest form, a demand meter has a gauge whose pointer moves a marker. While the gauge falls back, friction remains the marker in place. While a demand meter is read, its marker is reset, commonly along with a magnet from outside the sealed meter enclosure. Computerized demand meters commonly search the fifteen-minute interval in the month along with maximum demand (MD). Frequent they also record a month worth of fifteen-minute averages. A few demand meters measure the temperature of a conductor, or same as the heating of the conductor, in sequence to track "running" demand. Running demand meters commonly log the times while a maximum demand is exceeded, or they log the times while the meter enters a various tariff rate.
Electricity cannot be stored, so electricity retailers require arranging the essential generators to meet the maximum demand. Latest generators are long-term capital investments, so demand also straight affects the retailers' and power-providers' accounting, and required for long-term debt. In particular, although interest rates are high, producing companies are reluctant to install new capacity, and required customers to decrease demand, so the retailers use meters to detect and surcharge high demand.