Abstract: An apparatus for measuring a blood parameter comprising a red light source and an infrared light source for directing light toward a blood-receiving location and a detector, for receiving light from the first and second light sources which has been back scattered by the blood. The intensity of the first light source is adjusted so that the intensity of light at the detector from the first light source remains substantially constant over a range of values of the blood parameter and the intensity of the second light source is adjusted so that the intensity of light at the detector from the second light source is substantially constant over a range of values of the blood parameter. A signal is provided which is related to the intensity of one or both of the light sources and which provides an indication of the blood parameter. A circuit is provided to compensate for errors resulting from the light sources.

Abstract: A cuvette comprising a housing having a passage therethrough and being adapted to receive blood. The housing has a wall with an outer face. An optical window leads from the outer face to the passage and the optical window is transmissive to an optical signal so that a parameter of blood in the passage can be measured. A magnet is carried by the wall and spaced from the optical window for use in providing information about the cuvette. The cuvette is releasably attachable to an optical head. The optical head includes a plurality of Hall effect transducers which respond to the position of the magnet on the housing so that the position of the magnet can be used to provide information about the cuvette.