This book predates modern statistical software but it is still entirely worthwhile for people who need to know the "why and how" of ANCOVA. The text is built around interesting examples and several small data sets. The writing is exceptionally good and supports the basic algebra. So, if you are not a math person you can read around the formulas without a break in the continuity. If you want descriptions of the algebra it is all here also. By modern standards there are few graphics but they are superb and the plot showing adjusted group means makes the book worth buying.The only down side is that there are not explanations in R, SAS or SPSS. If you need coverage in SAS get Walker's Common Statistical Methods.