Ampère's law as stated above describes a physical property of the world. However, the choices about the form of "k"m and the value of "μ"0 are totally human decisions, taken by international bodies composed of representatives of the national standards organizations of all participating countries. The parameter "μ"0 is a measurement-system constant, not a physical constant that can be measured. It does not, in any meaningful sense, describe a physical property of the vacuum. This is why the relevant Standards Organizations prefer the name "magnetic constant", rather than any name that carries the hidden and misleading implication that "μ"0 describes some physical property.