Practical three way calibration This book is about chemometrics. In general terms chemometrics has the purpose of extracting information from chemical systems by a suitable combination of mathematics statistics and computer science. It is usually applied to solve chemical problems which can be primarily classified as either descriptive or predictive. In descriptive applications properties of chemical systems are modeled with the aim of learning underlying relationships and structure in most cases with a classification scheme in mind i.e. discriminating objects as belonging to a given class. In predictive applications on the other hand the emphasis is on modeling the properties of chemical systems with the purpose of predicting them in new unknown specimens. Analytical calibration belongs to this latter type of problems where the property of interest is typically the concentration of one or more selected analytes in a sample