The pieces' strength is closely related with their global mobility. Let us make a small mathematical experiment. We take each of the chess pieces (with the exception of the king and the pawn) and place it successively on all the 64 squares, counting the moves available from each square if the board is empty. The sum of all the possible legal moves for each piece separately gives us a number that we can consider, for abstract reasons only, the intrinsic value of the piece. For instance, the simplest case is that of the rook, which has 14 moves available from any square, which gives us R = 64 x 14 = 896.