Mechanical analyses of sediments are studied by comparison with other analyses. Both graphical and numerical methods of comparison are in use, each kind having its limitations. Two terms of a Gram-Charlier series, expressed in Krumbein's phi units, represent the data in many types of analyses, thus enabling them to be reduced to three numerical values or parameters. Graphical methods are given for recognizing such analyses, for obtaining the parameters, and for evaluating the extent to which they summarize the analytical information. A general procedure is outlined for systematic interpretation of mechanical analyses. The advantages of this method of interpretation are shown by considering in detail the information that can be deduced from the graphical study of a sieve analysis of a dune sand.