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The original is a unit of energy, equal to the energy in one mole (1 mol) of photons. The second is a unit of amount of photons, equal to one mole (1 mol) of photons. The rayleigh (R) is a unit of photon flux rate density equal to 10 10 m −2 ⋅s −1 (10 4 mm −2 ⋅s −1).
A Dictionary of Units of Measurement; Old units of measure; Measures from Antiquity and the Bible Antiquity and the Bible at the Wayback Machine (archived May 10, 2008) Reasonover's Land Measures A Reference to Spanish and French land measures (and their English equivalents with conversion tables) used in North America; The Unified Code for ...
The conversion between different SI units for one and the same physical quantity is always through a power of ten. This is why the SI (and metric systems more generally) are called decimal systems of measurement units. [10] The grouping formed by a prefix symbol attached to a unit symbol (e.g. ' km ', ' cm ') constitutes a new inseparable unit ...
In the SI system and generally in older metric systems, multiples and fractions of a unit can be described via a prefix on a unit name that implies a decimal (base-10), multiplicative factor. The only exceptions are for the SI-accepted units of time (minute and hour) and angle (degree, arcminute, arcsecond) which, based on ancient convention ...
A unit of measurement, or unit of measure, is a definite magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same kind of quantity. [1] Any other quantity of that kind can be expressed as a multiple of the unit of measurement. [2] For example, a length is a physical quantity.
Conversion of units is the conversion of the unit of measurement in which a quantity is expressed, typically through a multiplicative conversion factor that changes the unit without changing the quantity. This is also often loosely taken to include replacement of a quantity with a corresponding quantity that describes the same physical property.
A metric prefix is a unit prefix that precedes a basic unit of measure to indicate a multiple or submultiple of the unit. All metric prefixes used today are decadic.Each prefix has a unique symbol that is prepended to any unit symbol.
The measurement of time is unique in SI in that while the second is the base unit, and measurements of time smaller than a second use prefixed units smaller than a second (e.g. microsecond, nanosecond, etc.), measurements larger than a second instead use traditional divisions, including the sexagesimal-based minute and hour as well as the less ...