DDSY989 is a new kind of static single-phase prepayment watt-hour meter developed with the latest technology. It is used to measure 50/60Hz single-phase AC active energy. It is an ideal product to change the way of using electricity. With the practice of selling the power by card it can control the using of power conveniently. All the specifications are up to the standard IEC 1036-96 JB/T 8382-96.