The ampere is the SI unit of electric current. It is defined by taking the fixed
numerical value of the elementary charge e to be 1.602 176 634 × 10⁻¹⁹ when expressed
in the unit C, which is equal to A s, where the second is defined in terms of
∆νCs.
The second is the SI unit of time. It is defined by taking the fixed numerical value of
the caesium frequency ∆νCs, the unperturbed ground-state hyperfine
transition frequency of the caesium 133 atom, to be 9 192 631 770 when expressed in the
unit Hz, which is equal to s⁻¹.