Ampere Ampere The ampere (; symbol: A), often shortened to "amp", is the base unit of electric current in the International System of Units (SI). It is named after André-Marie Ampère (1775–1836), French mathematician and physicist, considered the father of electrodynamics. The International System of Units defines the ampere in terms of other base units by measuring the electromagnetic force between electrical conductors carrying electric current. The earlier CGS measurement system had two different definitions of current, one essentially the same as the SI's and the other using electric charge as the base unit, with the unit of charge defined by
Rai (unit) Rai (unit) A rai (, ) is a unit of area equal to 1,600 square metres (16 ares, 0.16 hectares, 0.3954 acres), and is used in measuring land area for a cadastre or cadastral map. Its current size is precisely derived from the metre, but is neither part of nor recognized by the modern metric system, the International System (SI). The rai is defined as 1 square "sen" or (40 m × 40 m). It can be divided in four "ngaan" or 400 square "wa". It is commonly used in Thailand. Although recognized by the SI, its use is not