In measurement of non-faradaic admittance (or tensammetry), a plot of alternating current against applied potential shows a minimum or maximum when a non-electroactive substance undergoes adsorption or desorption at the surface of the indicator electrode. Such a maximum or minimum may be called an apex to emphasize its non-faradaic origin and distinguish it from a 'summit', which would result from a charge-transfer process. The highest value of the current on such an apex may be called an apex current, and the corresponding applied potential may be called an apex potential.