The unit ampere (A) is defined by fixing the electron charge e to be
1.602,176,634×10-19 C (= A·s),
where second is defined by the atomic clock.
History
Around 1910, the American physicist Robert Andrew Millikan (1868 - 1953),
with the help of his doctoral student Harvey Fletcher (1884 - 1981),
determined the charge of the electron in the famous oil drop experiment.
The result 1.592×10-19 C is only 0.6% smaller than the value accepted today.
