Changes

Mass never changes. But in addition to the prototype meter changing its length over time, scientists later realized that water has different densities at different [[temperature|temperatures]].

Mass never changes. But in addition to the prototype meter changing its length over time, scientists later realized that water has different densities at different [[temperature|temperatures]].

Today, the standard [[kilogram]] is kept at the International Bureau of Standards headquarters in Sèvres. It remains today the only generally accepted unit of measurement based on an artifact. But the definition of the liter has now changed, and is no longer dependent on the length of the meter. Today, one liter is defined as the volume of one kilogram of water at four degrees [[Celsius]]. One milliliter is simply one-thousandth of this, and one milliliter of water at this temperature weighs one gram. But to say that one liter is "one thousand cubic centimeters" is no longer correct, simply because the definition of length has changed, while that of mass has not.

Today, the standard [[kilogram]] is kept at the International Bureau of Standards headquarters in Sèvres. It remains today the only generally accepted unit of measurement based on an artifact.

== Relation to other systems of measurement ==

== Relation to other systems of measurement ==