chapter 1 Introduction -- chapter 2 Abstract Geometrical and Mechanical Representations -- chapter 3 Mechanical Models for Multidimensional Medians -- chapter 4 Method of Least Squared Deviations -- chapter 5 Method of Least Absolute Deviation -- chapter 6 Minimax Absolute Deviation Method -- chapter 7 Method of Least Median of Squared Deviations -- chapter 8 Mechanical Models of Metric Graphs -- chapter 9 Categorical Data Analysis -- chapter 10 Method of Averages and Curve Fitting by Splines -- chapter 11 Multivariate Generalisations of the Method of Least Squares.