Three types of zero‐crossing measurements—(i) average zero‐crossing rate, (2) density of time intervals between zero‐crossings, and (3) excess‐threshold duration—are related theoretically. It is shown that measurement types 1 and 3 can be derived from the type 2 measurement. Measurement types 1 and 3 cannot be directly related, but it is shown that the type 2 measurement can be derived from the type 3 measurement.