Ampere W/V. Current can be measured by a multimeter, a device that can measure electrical voltage, current, and resistance. The standard ampere is most accurately realized using a Kibble balance, but is in practice maintained via Ohm's law from the units of electromotive force and resistance, the volt and the ohm, since the latter two can be tied to physical phenomena that are relatively easy to reproduce, the Josephson junction and the quantum Hall effect, respectively. At present, techniques to establish the realization of an ampere have a relative uncertainty of approximately a few parts in 10, and involve realizations of
Ground loop (electricity) the cable If a current "I" from a separate source is flowing through the ground conductor, the resistance "R" of the conductor will create a voltage drop along the cable ground of "IR", so the destination end of the ground conductor will be at a different potential than the source end Since the differential amplifier has high impedance, little current flows in the signal wire, therefore there is no voltage drop across it: formula_15 The ground voltage appears to be in series with the signal voltage "V" and adds to it If "I" is an AC current this can result