<Li> The hitting area, composed of the strings, must be flat and generally uniform . </Li> <Li> The frame of the hitting area may not be more than 29 inches (74 cm) in length and 12.5 inches (32 cm) in width . </Li> <Li> The entire racket must be of a fixed shape, size, weight, and weight distribution . There may not be any energy source built into the rackets . </Li> <Li> The rackets must not provide any kind of communication, instruction or advice to the player during the match . </Li>

How many minutes is a set in tennis