A method for non-invasively determining a blood oxygen saturation level within a subject's tissue using a near infrared spectrophotometric sensor capable of transmitting a light signal into the tissue of a subject and sensing the light signal at a predetermined distance once it has passed through the tissue via transmittance or reflectance, said method comprising the steps of: transmitting a light signal into the subject's tissue using a light source of the sensor, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength; sensing a first intensity of the light signal using a first light detector of the sensor at a first predetermined distance and sensing a second intensity of the light signal using a second light detector of the sensor at a second predetermined distance from the light source, comprising sensing at the first, second, and third wavelengths after the light signal travels through the subject, wherein the first intensity sensed at the first predetermined distance after the light signal travels through the subject comprises of attenuation and energy loss from both deep and shallow tissue and wherein the second intensity sensed at the second predetermined distance after the light signal travels through the subject comprises of attenuation and energy loss from shallow tissue; and, with a processor: determining an attenuation of the light signal for each of the first, second, and third wavelengths using the sensed first intensity and sensed second intensity at the first, second, and third wavelengths; determining a difference in the attenuation of the light signal between the first wavelength and the second wavelength, and between the first wavelength and the third wavelength; cancelling out or minimizing the energy losses due to: light scattering within the tissue; other background absorption losses from biological compounds; and other losses including measuring apparatus variability, by determining differential attenuation as a function of wavelength; and determining the blood oxygen saturation level within the subject's tissue using the difference in attenuation between the first wavelength and the second wavelength, and the difference in attenuation between the first wavelength and the third wavelength. transmitting a light signal into the subject's tissue using a light source of the sensor, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength; sensing a first intensity of the light signal using a first light detector of the sensor at a first predetermined distance and sensing a second intensity of the light signal using a second light detector of the sensor at a second predetermined distance from the light source, comprising sensing at the first, second, and third wavelengths after the light signal travels through the subject, wherein the first intensity sensed at the first predetermined distance after the light signal travels through the subject comprises of attenuation and energy loss from both deep and shallow tissue and wherein the second intensity sensed at the second predetermined distance after the light signal travels through the subject comprises of attenuation and energy loss from shallow tissue; and, with a processor: determining an attenuation of the light signal for each of the first, second, and third wavelengths using the sensed first intensity and sensed second intensity at the first, second, and third wavelengths; determining a difference in the attenuation of the light signal between the first wavelength and the second wavelength, and between the first wavelength and the third wavelength; cancelling out or minimizing the energy losses due to: light scattering within the tissue; other background absorption losses from biological compounds; and other losses including measuring apparatus variability, by determining differential attenuation as a function of wavelength; and determining the blood oxygen saturation level within the subject's tissue using the difference in attenuation between the first wavelength and the second wavelength, and the difference in attenuation between the first wavelength and the third wavelength. determining an attenuation of the light signal for each of the first, second, and third wavelengths using the sensed first intensity and sensed second intensity at the first, second, and third wavelengths; determining a difference in the attenuation of the light signal between the first wavelength and the second wavelength, and between the first wavelength and the third wavelength; cancelling out or minimizing the energy losses due to: light scattering within the tissue; other background absorption losses from biological compounds; and other losses including measuring apparatus variability, by determining differential attenuation as a function of wavelength; and determining the blood oxygen saturation level within the subject's tissue using the difference in attenuation between the first wavelength and the second wavelength, and the difference in attenuation between the first wavelength and the third wavelength.