Chemometrics is not intrisically difficult to understand, but it has a high barrier especially for beginners. One of the reasons may be that most of tutorials employses unnecessarily many equations, and they describe claculation algorithms too much. Nonetheless, the basic concept of PCR and PLS should be described on the line of CLS and ILS. The discovery of advantage of ILS, and the idea of using latent variables by PCA are the most important to fully understand PCR and PLS. Richard Kramer writes the book along this concept, and we can comprehensively understand the ideas of maltivariate analysis of spectra. He uses many figures, as if we were performing simulations by ourself. After fully understanding of this book, we would understand other tutorials more deeply and easily.