How does the eddy current error and hysteresis error of the electromagnetic system instrument cause?

The hysteresis error is the error produced when the electromagnetic system instrument is used in the AC circuit. For the ammeter, the alternating magnetic field of the metal parts in the instrument is used to generate eddy current, and the mutual inductance between the coil and the coil has a degaussing effect on the magnetic field of the coil, which results in the deflection of the instrument and hence the error of the eddy current. The hysteresis error is the error produced when the electromagnetic system instrument is used in the DC circuit. It is caused by the magnetic hysteresis of iron core, magnetic shield and ferromagnetic material near the measuring mechanism.