Thus the centi-ampere balance ranges from i to ioo centi-amperes, the deci-ampere balance from i to ioo deci-amperes, the ampere balance from i to ioo amperes, the deka-ampere balance from i to ioo amperes, the hecto-ampere balance from 6 to 600 amperes, and the kilo-ampere balance from ioo to 2500 amperes.
A third platinum coil, wound non-inductively between the primary and the secondary, served to carry the current by which the ring was heated; a current of 4.6 amperes, with 16 volts across the terminals, was found sufficient to maintain the ring at a temperature of 11 50° C. In the ring itself was embedded a platinum-thermometer wire, from the resistance of which the temperature was determined.
At first the current is 3000 amperes at 220 volts, increasing to 9000 amperes at 20 volts after 20 hours.
If then the amperemeter scale reading was 100 it would show an error of that scale reading of minus 1.9 amperes or nearly 2%.
The principle on which the instrument works is as follows: Suppose any circuit, such as an electric motor, lamp or transformer, is receiving electric current; then the power given to that circuit reckoned in watts is measured by the product of the current flowing through the circuit in amperes and the potential difference of the ends of that circuit in volts, multiplied by a certain factor called the power factor in those cases in which the circuit is inductive and the current alternating.