Beers law of light states that the extinction coefficient plus concentration plus path length equals absorption. The extinction coeffcient, or light absorbance, varies with each hemoglobin attachment. Carboxyhemoglobin (COHb) is CO bound to hemoglobin and is read as oxyhemoglobin (HbO2), O2 bound to hemoglobin, so the saturation read by the pulse oximeter is falsely high. Methemoglobin (MetHb) absorbs equal amounts of red and near infrared light. Methamoglobin is read as reduced hemoglobin so the saturation read by the pulse oximeter is falsely low.