The flexible clamp power meter adopts the advanced Rockwell Coil (or Rogowski Coil) technology, which is a toroidal coil that is uniformly wound on a non-ferromagnetic material. This technology not only significantly reduces the hysteresis losses, but also has almost zero phase error, no magnetic saturation, extremely high linearity, and strong anti-interference ability. The output signal is the derivative of current against time. By integrating the output voltage signal, the input current can be almost exactly replicated. The test current range can be from milliamps range to tens of thousands of amperes.