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Conversions between units in the metric system are defined by their prefixes (for example, 1 kilogram = 1000 grams, 1 milligram = 0.001 grams) and are thus not listed in this article. Exceptions are made if the unit is commonly known by another name (for example, 1 micron = 10 −6 metre).
For example, in the 1930s Widmark measured alcohol and blood by mass, and thus reported his concentrations in units of g/kg or mg/g, weight alcohol per weight blood. Blood is denser than water and 1 mL of blood has a mass of approximately 1.055 grams, thus a mass-volume BAC of 1 g/L corresponds to a mass-mass BAC of 0.948 mg/g.
For example, it is 7.62 ml (6 grams) of alcohol in Austria, but in Japan it is 25 ml (19.75 grams): In the United Kingdom, there is a system of units of alcohol which serves as a guideline for alcohol consumption. A single unit of alcohol is defined as 10 ml. The number of units present in a typical drink is sometimes printed on bottles.
For example, milligram (mg) is used instead of microkilogram (μkg). During mathematical operations, prefixes are treated as multiplicative factors. For example, 5 km is treated as 5000 m, which allows all quantities based on the same unit to be factored together even if they have different prefixes.
The unit of time should be the second; the unit of length should be either the metre or a decimal multiple of it; and the unit of mass should be the gram or a decimal multiple of it. Metric systems have evolved since the 1790s, as science and technology have evolved, in providing a single universal measuring system.
The name "katal" has been used for decades. The first proposal to make it an SI unit came in 1978, [6] [10] and it became an official SI unit in 1999. [6] [11] [12] The name comes from the Ancient Greek κατάλυσις (katalysis), meaning "dissolution"; [13] the word "catalysis" itself is a Latinized form of the Greek word. [13] [14]
Although there are examples to the contrary, it should be stressed that the commonly used "units" of % w/v are grams per millilitre (g/mL). 1% m/v solutions are sometimes thought of as being gram/100 mL but this detracts from the fact that % m/v is g/mL; 1 g of water has a volume of approximately 1 mL (at standard temperature and pressure) and ...
However, the names of all SI mass units are based on gram, rather than on kilogram; thus 10 3 kg is a megagram (10 6 g), not a *kilokilogram. The tonne (t) is an SI-compatible unit of mass equal to a megagram (Mg), or 10 3 kg. The unit is in common use for masses above about 10 3 kg and is often used with SI prefixes.