A method of calibrating a spectrographic inspection system, comprises providing a plurality of packages, each of the plurality of packages containing a group of items, wherein each of the groups of items has a known composition, measuring the reflectance value of each of the groups of items and thereby obtaining a reference reflectance value set, normalizing the reference reflectance value set and thereby creating a normalized reference reflectance value set, and storing the normalized reference reflectance value set.