These meters have electronic measurement circuits but show is by impulse counters/stepper motors. Accuracy is classically class 1.0 or 2.0 and commonly these meters cater to limited tariffs applicable mostly to single phase or 3-phase direct linked segment.
In 1885, Galileo Ferraris discovered which while a solid disc is placed in an out-of-phase AC magnetic field; it rotates at a rate proportional to the flow of electrical energy in the coils which produced the field. This discovery, made over a century ago, is the principle on that the great majority of electromechanical energy meters still operate present. The principle is easy: a solid disc is mounted on jeweled bearings and permitted to rotate freely in a sealed container. AC flowing by the coils in the meter sets up an alternating magnetic field that is proportional to the amount of power flowing by the meter. As the armature rotates in the magnetic field, a counter detects the number of revolutions made through the disk.