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The amount of substance, symbol n, of a system is a measure of the number of specified elementary entities. An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles." [1] Atomic weight or molecular weight divided by the molar mass constant, 1 g/mol. N candela: cd luminous intensity
The SI comprises a coherent system of units of measurement starting with seven base units, which are the second (symbol s, the unit of time), metre (m, length), kilogram (kg, mass), ampere (A, electric current), kelvin (K, thermodynamic temperature), mole (mol, amount of substance), and candela (cd, luminous intensity).
This set U is sometimes called the universe of discourse. × (multiplication sign) See also × in § Arithmetic operators. 1. Denotes the Cartesian product of two sets. That is, is the set formed by all pairs of an element of A and an element of B. 2.
The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum. zeptosecond: 10 −21 s: One sextillionth of a second. Time measurement scale of the NIST and JILA strontium atomic clock. Smallest fragment of time currently measurable is 247 zeptoseconds. [3] attosecond: 10 −18 s: One quintillionth of a second ...
A function (which in mathematics is generally defined as mapping the elements of one set A to elements of another B) is called "A onto B" (instead of "A to B" or "A into B") only if it is surjective; it may even be said that "f is onto" (i. e. surjective). Not translatable (without circumlocutions) to some languages other than English.
A unit of measurement that applies to money is called a unit of account in economics and unit of measure in accounting. [5] This is normally a currency issued by a country or a fraction thereof; for instance, the US dollar and US cent (1 ⁄ 100 of a dollar), or the euro and euro cent.
A base unit of measurement (also referred to as a base unit or fundamental unit) is a unit of measurement adopted for a base quantity. A base quantity is one of a conventionally chosen subset of physical quantities , where no quantity in the subset can be expressed in terms of the others.
A notable exception is that for a large measure of seconds, the non-SI units of minute, hour and day are customary instead. Units of duration longer than a day are problematic since both month and year have varying number of days. Sub-second measures are often indicated via submultiple prefixes. For example, millisecond. [4]