Many measuring devices measure because magnetic and electric fields provide forces proportional to the intensity of their field. By using a tension spring against which the magnetic or electric force may pull or push, a movable needle may be produced. The needle may then be placed in front of a calibrated measuring scale, taking a direct reading of the quantity to be calculated. These meters behave as means of electrostatic deflection or electromagnetic deflection.
Sometimes, electric current is calculated by the extent of heat it gives in a resistance. Such meters act by thermal heating rules. Some meters work by means of small motors whose speed lies on the calculated quantity. The rotation rate, or the number of rotations in a provided time, may be calculated or counted. These are types of rate meters. Still other types of meters actually count electronic pulses, as in thousands, millions or billions. These are electronic counters. There are also several other metering procedures.
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