SI base unit referenced to the values of the fundamental constants, namely the Planck constant ("h"), the electron charge ("e"), the Boltzmann constant ("k"), and the Avogadro constant ("N"). This approach was approved in 2018, only after measurements of these constants were achieved with sufficient accuracy. SI base unit The International System of Units (SI) defines seven units of measure as a basic set from which all other SI units can be derived. The SI base units and their physical quantities are the meter for measurement of length, the kilogram for mass, the second for time, the ampere for electric current, the kelvin
Rai (unit) encouraged. The word "rai" also means plantation. 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