systems and methods are disclosed for non - invasively measuring blood glucose levels in a biological sample based on spectral data . a variety of techniques are disclosed for improving signal - to - noise ratio in the acquisition of spectral data and calculating attenuance of light attributable to blood in a sample . disclosed techniques include using a standard deviation operation in conjunction with the logarithm function , using a normalization factor , using a ratio factor , accounting for the effect of temperature on various system components such as resistors , and accounting for dark current in a light detector by performing a calibration .