[2] It can be expressed in terms of SI base units (m, kg, s, and A) as Equivalently, it is the potential difference between two points that will impart one joule of energy per coulomb of charge that passes through it.Historically the "conventional" volt, V90, defined in 1987 by the 18th General Conference on Weights and Measures[3] and in use from 1990 to 2019, was implemented using the Josephson effect for exact frequency-to-voltage conversion, combined with the caesium frequency standard.[4] Empirically, several experiments have shown that the method is independent of device design, material, measurement setup, etc., and no correction terms are required in a practical implementation.Ohm's Law is analogous to the Hagen–Poiseuille equation, as both are linear models relating flux and potential in their respective systems.Nominal voltages of familiar sources: In 1800, as the result of a professional disagreement over the galvanic response advocated by Luigi Galvani, Alessandro Volta developed the so-called voltaic pile, a forerunner of the battery, which produced a steady electric current.