A system of electrical units in the c.g.s. system (see c.g.s. units). The e.s.u. of electric charge is the statcoulomb (all e.s.u. have the prefix stat- attached to the names of practical units). The statcoulomb is the quantity of electric charge that will repel an equal quantity 1 centimetre distant with a force of 1 dyne. In e.s.u. the electric constant is of unit magnitude. The system has now been replaced for most purposes by SI units. Compare electromagnetic units; Gaussian units; Heaviside–Lorentz units.