Millikan and Harvey Fletchers oil-drop experiment

The original experiment was performed in the year 1909 through Robert Millikan and Harvey Fletcher through balancing the downward gravitational force and the upward electrical and buoyant forces of charged oil droplets suspended among two metal plates. The mass of the droplets and the density of the oil was called, so the gravitational and buoyant forces could be computed from the measured radii of the oil drops. 

Since the electric field was known, the charge on the oil drops could be denoted while the drops were held at equilibrium. The value for the charge was computed for several droplets. The values were multiples of the value of a charge of a single electron. Millikan and Fletcher calculated the charge of an electron to be 1.5924(17)×10^-19 C. Their value was within one percent of the presently accepted value for the charge of an electron, that is 1.602176487(40)×10^-19 C.