In order to establish the numerical value of ε 0, one makes use of the fact that if one uses the rationalized forms of Coulomb's law and Ampère's force law (and other ideas) to develop Maxwell's equations, then the relationship stated above is found to exist between ε 0, μ 0 and c 0. In principle, one has a choice of deciding whether to make the coulomb or the ampere the fundamental unit of electricity and magnetism. The decision was taken internationally to use the ampere. This means that the value of ε 0 is determined by the values of c 0 and μ 0, as stated above. For a brief explanation of how the value of μ 0 is decided, see Vacuum permeability.