Pulse oximeter sensor with piece-wise function

An oximeter system comprising an oximeter sensor in communication with an oximeter and a light detector signal. The oximeter sensor comprises a light emitter for directing light at a patient; a light detector mounted to receive light from the patient; and a memory storing a plurality of values of oxygen saturation or signal ratiometric values used to determine oxygen saturation. These values are dependent on a mean wavelength of the light emitter. The oximeter is programmed to determine oxygen saturation from the light detector signal by fitting the oxygen saturation to a curve defined by the values stored in the memory.