1. A quantitative analysis instrument for measuring an unknown attribute level based on an indirect measurement of a biological sample, said instrument comprising: a. a source of infrared energy generating multiple wavelengths; b. an input sensor element for directing said wavelengths of infrared energy into said biological sample and an output sensor element for collecting at least a portion of the diffusely reflected infrared energy from said biological sample, said input and said output sensor elements adapted to optically couple to said biological sample; c. at least one detector arranged for measuring the intensities of at least a portion of said wavelengths collected by said output sensor element; and d. means for processing said master calibration information, said reference measurement information, and said indirect measurement information to generate a prediction of said unknown attribute level.