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A physiological set point is a reference around which regulation is organized, analogous to a reference signal. An observed average is not automatically a separately encoded target. A range of acceptable values and different response thresholds can be more informative than a single exact number. Negative feedback describes a causal sign; neither perfect constancy nor complete restoration follows from that sign alone.

For core body temperature, circadian rhythms and fever can change the defended level. Thus a response toward the current physiological set point need not restore yesterday's temperature. A drifting target and imperfect tracking of a fixed target are different explanations for a changing readout. ^[ref]