1. A method determining a blood parameter of pulsing blood, the method comprising: receiving first and second intensity signals from a light-sensitive detector which detects light of at least first and second wavelengths attenuated by body tissue carrying pulsing blood; representing the first and second intensity signals mathematically in a manner which corresponds to graphically representing magnitudes of ones of the first intensity signals with magnitudes of ones of the second intensity signals on axes of a graph; and determining blood oxygen saturation of the pulsing blood using the representation.