You may know the modern "system" of chessmen values but some aren`t known.The king can be given a value of 4 but normally is priceless.The queen`s highest value was 13.5 and the lowest 7.9.(The chessmen values can go into mixed decimals)The rook`s highest was 7 and the lowest was 4.5. The bishop`s value stayed within the 3-4 range while the knight`s value range was 2.4 -3.5.
The bishops are worth higher in open postions and knights are higher in closed postions.
http://en.wikipedia.org/wiki/Chess_piece_relative_value is the site to look at.(I am avoiding plaigarism)