BOOK 7 - CALCULATION PROBLEMS
 All chess is imbued with analysis and calculation. Combinations and tactical play in particular require a high degree of calculation. We're talking about those positions where, given the acute nature of the battle, the value of each tempo is crucial or very high.
 Calculation was specifically studied in Chapter 6 of Chess School 2, Reading the Position, and more specifically in its Section 4, Calculating Variants.
 The student should bear in mind that when solving the exercises he is not asked to decipher every single move in the game (which are sometimes included until the end, for documentary purposes), but only those that lead, for example, to a decisive advantage for one side (+ -, - +) or to a forced draw (=), if appropriate. There are exceptions (and in this sense the guidance of an instructor or the reader's own common sense is important), because if the first move or two produce such a judgment, the solver is expected to provide additional concrete lines that enrich the solution. Chess is not a mathematical science and allows different interpretations.
 Only one formula is known for progress in chess: play as many games as possible, together with theoretical study and analysis of the games themselves. The ideal complement to this formula, as many great masters recommend, is for the player to develop and perfect his tactical and strategic skills by solving numerous exercises, specially selected for their usefulness. Like the ones we offer here.