Mole (unit) and growth chamber lighting for plants is sometimes expressed in micromoles per square meter per second, where 1 mol photons = photons. In 2011, the 24th meeting of the General Conference on Weights and Measures (CGPM) agreed to a plan for a possible revision of the SI base unit definitions at an undetermined date. The 26th meeting of the CGPM, in a formal vote on 16 November 2018, approved the proposed redefinition of SI base units mole, kilogram, ampere and kelvin. One mole of a substance will have exactly specified "elementary entities" of that substance. The definition of the mole
Grain (unit) cod. gr. ss tablets" (using the medical abbreviations ASA for aspirin, c̄ for "with", and cod. for codeine). The apothecaries' system has gradually been replaced by the metric system, and the use of the grain in prescriptions is now rare. Particulate emission levels, used to monitor and regulate pollution, are commonly measured in grains per cubic foot. This is the same unit commonly used to measure the amount of moisture in the air, also known as the absolute humidity. The SI unit used to measure particulate emissions and absolute humidity is mg/m. One grain per cubic foot is approximately .