Although the device might appear to be a simple machine, pulse oximeters are actually a very interesting option for measuring the oxygen saturation level of the blood. The way oxygen is measured by a pulse oximeter is through the measurement of light that is present in the blood since the level of red and infrared light is absorbed differently depending on how much oxygen is present. By emitting a beam of red light a pulse oximeter can measure how much oxygen is present by calculating the ratio of red to infrared light which will then be converted to an oxygen saturation level.