Millikan's oil drop experiment has showed that the electric charge
in oil drops is quantized, and has allowed a determination of its
value to 
. The experiment has
neither proved that the value of the fundamental electric unit is on
the order of 
nor that electric charge in itself
is quantized. All it has proved is that electric charge appears in
quanta of magnitude in oil droplets.
Other experiments which followed Millikan's
experiment, like Johnson's shot noise experiment, indicated the same
quantization of charge as the one found in this experiment. One might
therefore believe that the discussion on whether the charge is quantized in
quanta of 
or appears in quanta of
is a purely philosophical one, with little relevance
to physics. However, with the emergence of elementary particle physics,
it has been showed that there do exist particles with a lower charge
than the 'elementary' charge. These particles have a charge of 1/3 times
the elementary charge, but under 'normal' conditions they always appear
in groups of three, so the elementary charge unit in 'everyday physics' is
indeed the one observed above.
