The elementary charge is one of the fundamental physical constants, and accurate knowledge of its value is of great importance. His experiment measured the force on tiny charged droplets of oil suspended against gravity between two metal electrodes. Knowing the electric field, the charge on the droplet could be determined. Repeating the experiment for many droplets, Millikan showed that the results could be explained as integer multiples of a common value (1.592 × 10 coulomb), which is the charge of a single electron. That this is somewhat lower than the modern value of 1.602 176 53(14) x 10 coulomb is probably due to Millikan's use of an inaccurate value for the viscosity of air.