In chess, a relative value (or point value) is a standard value conventionally assigned to each piece. Piece valuations have no role in the rules of chess but are useful as an aid to assessing a position. Valuation systems almost always assign a value of 1 point to the pawn, typically as its average value in the starting position. The best known system assigns 1 point to a pawn, 3 points to a knight or bishop, 5 points to a rook and 9 points to a queen. Valuation systems provide only a rough idea of the state of play. The actual value of a piece depends on the game situation and can differ considerably from the standard valuation. A well posted bishop may be more valuable than a passive rook, while a badly placed piece may be completely trapped and thus almost worthless. Chess engines conventionally output their assessment of a position in terms of 'centipawns' (cp), where 100 cp = 1 pawn. In addition to the balance, this assessment incorporates strategic features of the position . Standard valuations The following table is the most common assignment of point values. The oldest derivation of the standard values is due to the Modenese School (Ercole del Rio, Giambattista Lolli, and Domenico Lorenzo Ponziani) in the 18th century and is partially based on the earlier work of Pietro Carrera. The value of the king is undefined as it cannot be captured, let alone traded, during the course of the game. Chess engines usually assign the king an arbitrary large value such as 200 points or more to indicate that the inevitable loss of the king due to checkmate trumps all other considerations. The endgame is a different story, as there is less danger of checkmate, allowing the king to take a more active role. The king is good at attacking and defending nearby pieces and pawns. It is better at defending such pieces than the knight is, and it is better at attacking them than the bishop is. Overall, this makes it more powerful than a minor piece but less powerful than a rook, so its fighting value is worth about four points. This system has some shortcomings. Combinations of pieces do not always equal the sum of their parts; for instance, two bishops are usually worth slightly more than a bishop plus a knight, and three (nine points) are often slightly