Watt within the then-existing system of practical units as "the power conveyed by a current of an Ampère through the difference of potential of a Volt." In October 1908, at the International Conference on Electric Units and Standards in London, so-called "international" definitions were established for practical electrical units. Siemens' definition was adopted as the "international" watt. (Also used: 1 ampere x 1 ohm.) The watt was defined as equal to 10 units of power in the "practical system" of units. The "international units" were dominant from 1909 until 1948. After the 9th General Conference on Weights and Measures in 1948,
Negative resistance be defined, but the resistance is not constant; it varies with the voltage or current through the device. The resistance of such a nonlinear device can be defined in two ways, which are equal for ohmic resistances: Negative resistance, like positive resistance, is measured in ohms. Conductance is the reciprocal of resistance. It is measured in siemens (formerly "mho") which is the conductance of a resistor with a resistance of one ohm. Each type of resistance defined above has a corresponding conductance It can be seen that the conductance has the same sign as its corresponding resistance: a negative resistance