 In addition to points for pieces, most evaluation functions take many factors into account, such as pawn structure, the fact that a pair of bishops are usually worth more, centralized pieces are worth more, and so on.The protection of kings is usually considered, as well as the phase of the game (opening, middle or endgame).The output of the evaluation function is a single scalar, quantized in centipawns or other units, which is a weighted summation of the various factors described.