The program "OTOS: Obtaining tissue oxygen saturation" is an algorithm that obtains tissue oxygen saturation from in-vivo measurements of diffuse reflectance of the skin, measured with the ocean optics USB-4000 spectrophotometer, at two wavelengths . One corresponds to the near infrared and the other is a wavelength in the visible range, but the latter is selected based on the volunteer's melanin concentration, so the result is independent of skin type.