A method for measuring the level of a selected molecule in a target sample comprising: generating a first light of wavelength F1 and illuminating a portion of the sample with the first light; developing a first set of measured light intensity values by capturing a first scattered light from the target sample, directing the first scattered light to a plurality of light sensors (42, 44, 46, 48), each light sensor measuring light at a different wavelength, that wavelength being proximate to a wavelength of an expected Raman shift wavelength for the molecule in the sample, thereby obtaining a measurement from each of the light sensors, each measurement being specific to the first scattered light to that light sensor; generating a second light of wavelength F2 different in frequency from the first light and illuminating a portion of the sample with the second light; developing a second set of measured light intensity values by capturing a second scattered light from the sample, directing the second scattered light to the plurality of light sensors (42, 44, 46, 48), each light sensor measuring light at a different wavelength that wavelength being proximate to a wavelength of an expected Raman shift wavelength for the molecule in the sample, thereby obtaining a measurement from each of the light sensors, each measurement being specific to the second scattered light to that light sensor; characterised by: deriving from the first and second sets of measured light intensity values a value representing the level of a selected molecule in a target sample by steps comprising computing ratios of equivalent measured light intensity data from the first and second sets of measured light intensity values and interpolating by curve fitting to find a curve that passes through the endpoints on a wavelength ratio graph and, at two different measurement wavelengths between the endpoints of the graph, the curve is equidistant from the light intensity ratio values computed for such two different measurement wavelengths, where the equidistance value D represents a measure of the difference between the ratios of the measurements from the light sensors when a Raman signal is present and when it is not. generating a first light of wavelength F1 and illuminating a portion of the sample with the first light; developing a first set of measured light intensity values by capturing a first scattered light from the target sample, directing the first scattered light to a plurality of light sensors (42, 44, 46, 48), each light sensor measuring light at a different wavelength, that wavelength being proximate to a wavelength of an expected Raman shift wavelength for the molecule in the sample, thereby obtaining a measurement from each of the light sensors, each measurement being specific to the first scattered light to that light sensor; generating a second light of wavelength F2 different in frequency from the first light and illuminating a portion of the sample with the second light; developing a second set of measured light intensity values by capturing a second scattered light from the sample, directing the second scattered light to the plurality of light sensors (42, 44, 46, 48), each light sensor measuring light at a different wavelength that wavelength being proximate to a wavelength of an expected Raman shift wavelength for the molecule in the sample, thereby obtaining a measurement from each of the light sensors, each measurement being specific to the second scattered light to that light sensor; deriving from the first and second sets of measured light intensity values a value representing the level of a selected molecule in a target sample by steps comprising computing ratios of equivalent measured light intensity data from the first and second sets of measured light intensity values and interpolating by curve fitting to find a curve that passes through the endpoints on a wavelength ratio graph and, at two different measurement wavelengths between the endpoints of the graph, the curve is equidistant from the light intensity ratio values computed for such two different measurement wavelengths, where the equidistance value D represents a measure of the difference between the ratios of the measurements from the light sensors when a Raman signal is present and when it is not.