May 20, 2019, the ampere is redefined such that the elementary charge (charge of electron or proton) would be equal to 1.602176634 × 10−19
ampere now μ0 is no longer equal to 4π × 10-7 weber per ampere-metre and must be experimentally measured. However, [μ0/4π × 10-7] is 1.00000000055