Chess strategy is the aspect of chess play concerned with evaluation of chess positions and setting goals and long-term plans for future play. While evaluating a position strategically, a player must take into account such factors as the relative value of the pieces on the board, pawn structure, king safety, position of pieces, and control of key squares and groups of squares (e.g. diagonals, open files, and individual squares). Chess strategy is distinguished from chess tactics, which is the aspect of play concerned with the move-by-move setting up of threats and defenses. Some authors distinguish static strategic imbalances (e.g. having more valuable pieces or better pawn structure), which tend to persist for many moves, from dynamic imbalances (such as one player having an advantage in piece ), which are temporary. This distinction affects the immediacy with which a sought-after plan should take effect. Until players reach the skill level of "master", chess tactics tend to ultimately decide the outcomes of games more often than strategy. Many chess coaches thus emphasize the study of tactics as the most efficient way to improve one's results in serious chess play. The most basic way to evaluate one's position is to count the total value of pieces on both sides. The point values used for this purpose are based on experience. Usually pawns are considered to be worth one point, knights and bishops three points each, rooks five points, and queens nine points. The fighting value of the king in the endgame is approximately four points. These basic values are modified by other factors such as the position of the pieces (e.g. advanced pawns are usually more valuable than those on their starting squares), coordination between pieces (e.g. a usually coordinates better than a bishop plus a knight), and the type of position (knights are generally better in with many pawns, while bishops are more powerful in ). Another important factor in the evaluation of chess positions is the pawn structure or pawn skeleton. Since pawns are the most immobile and least valuable of the pieces, the pawn structure is relatively static and largely determines the strategic nature of the position. Weaknesses in the pawn structure, such as isolated, doubled, or backward pawns and , once created, are usually permanent. Care must therefore be taken to avoid them unless they are compensated by another valuable asset, such as the possibility to develop an attack.