Avogadro constant
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In chemistry, the Avogadro constant, commonly denoted NA, is a conversion constant or ratio between an amount of substance and the number of particles that it contains. The particles in question are a
Jean Perrin in 1926
Josef Loschmidt
The International System of Units, internationally known by the abbreviation SI, is the modern form of the metric system and the world's most widely used system of measurement. It is the only system o
Avogadro constant
…of particles that it contains. The particles in question are any designated elementary entity, such as molecules, atoms, ions, or ion pairs. It is an SI defining constant with the exact value 6.02214076×1023 mol−1 (reciprocal mole). The numerical value of this constant when expressed in terms of the mole is known as the…
Silicon sphere for the Avogadro project used for measuring the Avogadro constant to a relative standard uncertainty of 2×10−8 or less, held by Achim Leistner
Stone marking the Austro-Hungarian/Italian border at Pontebba displaying myriametres, a unit of 10 km used in Central Europe in the 19th century (but since deprecated)
Closeup of the National Prototype Metre, serial number 27, allocated to the United States