1. A method of determining whether to include a signal in a determination of a physiological characteristic of pulsing blood, the method comprising: receiving a plurality of intensity signals from a light-sensitive detector which detects light of a plurality of wavelengths transmitted through body tissue carrying pulsing blood; determining an indication of correlation between at least two of the plurality of intensity signals; and based on the indication of correlation, determining whether to include one or more of the plurality of intensity signals in a determination of a physiological characteristic of pulsing blood.