A method for determining the most likely composition of a sample, including obtaining data from a sample, wherein the data includes a representation of a measured spectrum; determining the precision state of the representation of the measured spectrum; providing a plurality of library candidates and, for each library candidate, providing data representing each library candidate, wherein the data includes a representation of a library spectrum; determining a representation of the similarity of the sample to each library candidate using (i) the representation of the measured spectrum; (ii) the precision state of the representation of the measured spectrum; and (iii) the representation of the library spectrum for that library candidate; determining the most likely composition of the sample based upon the determined representations of similarity of the sample to each library candidate; and displaying the most likely composition of the sample to a user.