Obtaining two spectra from the same sample under two different conditions at about the same time for comparison, where at least one of the spectra measures magnitudes of electromagnetic radiation on at least four different ranges or weightings of wavelengths or frequencies. Classifying a sample using these spectra obtained by a user, and using spectra obtained from different samples by different users to identify the sample. Computing correlations between data related to food and ingredient consumption by one or more users over time, and data related to passive personal log data, user entered feedback, user interaction data or personal information related to those users, and detecting: foods or ingredients to which a user may be allergic or intolerant a possible medical condition of a user a possible link between food and ingredient consumption and a medical or health condition or a similarity between at least two such users.
