IN electricity there exists an unsettled dispute concerning the nature of system variation, that is, the transition from one system to another. According to one of the parties in the dispute, system variation is caused by a variation of units, whereas the other party maintains that system variation is caused by a variation of quantities1,2. In a recent article3 I demonstrated that this variation consists in a change in the form of quantity equations without a change in quantities. As a consequence some units become incoherent and may be replaced by other units, which are now coherent with the changed equations. In the following a résumé of the problem in question is given.