1. In a signal processor, a method of determining measurements for one or more blood parameters of pulsing blood, the method comprising: receiving a first intensity signal from a light-sensitive detector which detects light of a first wavelength attenuated by body tissue carrying pulsing blood; receiving a second intensity signal from the light-sensitive detector which detects light of a second wavelength attenuated by body tissue carrying pulsing blood; electronically transforming the first and second intensity signals into the frequency domain; electronically determining values of the transformed first and second intensity signals that represent desired physiological data; electronically combining the transformed first and second intensity signals to form a composite signal comprising physiological information from both the transformed first and second intensity signals; and electronically analyzing the composite signal using one or more physiologically-based rules; and electronically determining the measurement of the blood parameter based at least in part on results of the analysis.