<P> The necessity of measuring the size of the oil droplets can be eliminated by using tiny plastic spheres of a uniform size . The force due to viscosity can be eliminated by adjusting the strength of the electric field so that the sphere hovers motionless . </P> <P> Any electric current will be associated with noise from a variety of sources, one of which is shot noise . Shot noise exists because a current is not a smooth continual flow; instead, a current is made up of discrete electrons that pass by one at a time . By carefully analyzing the noise of a current, the charge of an electron can be calculated . This method, first proposed by Walter H. Schottky, can determine a value of e of which the accuracy is limited to a few percent . However, it was used in the first direct observation of Laughlin quasiparticles, implicated in the fractional quantum Hall effect . </P> <P> Another accurate method for measuring the elementary charge is by inferring it from measurements of two effects in quantum mechanics: The Josephson effect, voltage oscillations that arise in certain superconducting structures; and the quantum Hall effect, a quantum effect of electrons at low temperatures, strong magnetic fields, and confinement into two dimensions . The Josephson constant is </P> <Dl> <Dd> K J = 2 e h (\ displaystyle K_ (\ mathrm (J)) = (\ frac (2e) (h))) </Dd> </Dl>

How many fundamental units of charge e is this