Circadian rhythm - Wikipedia, the free encyclopedia

Circadian rhythm - Wikipedia, the free encyclopedia: "Criteria

To be called circadian, a biological rhythm must meet these four general criteria:
The rhythms repeat once a day (they have a 24-hour period). In order to keep track of the time of day, a clock must be at the same point at the same time each day, i.e. repeat every 24 hours.
The rhythms persist in the absence of external cues (endogenous). The rhythm persists in constant conditions with a period of about 24 hours. The rationale for this criterion is to distinguish circadian rhythms from simple responses to daily external cues."

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