Blood flow measurement is based on the blood of hemoglobin to absorb light capacity. The sensors are made up of light sources and detectors placed close to each other, and are placed directly on the skin when measured. The emitted light penetrates into the skin, tissues and blood vessels, and then is absorbed, transmitted and reflected. The intensity of the reflected light recorded by the detector will vary depending on the flow of blood flowing through the arteries. The applicable wavelength for this measurement depends on which part of the body is measured.