The term "flat demand rate" applies to a charge for gas service based upon the customer's installation of gas-consuming devices. this is usually so much per mcf, therm, month, or year. Sometimes this type of rate is nominally so much per fixture (as gas lamps) per year or month but estimated demand and quantity of gas likely to be used play an important part in the determination. Such a rate may be modified by the "block" or "step" methods.