the game. There are four main types of courts depending on the materials used for the court surface: clay courts, hard courts, grass courts and carpet courts. The International Tennis Federation (ITF) lists different surfaces and properties and classifies surfaces into one of five pace settings: Category 1 (slow) Category 2 (medium-slow) Category 3 (medium) Category 4 (medium-fast) Category 5 (fast) Of the current four Grand Slam tournaments, the Australian and US Open use hard courts, the French Open is played on clay, and Wimbledon, the only Grand Slam to have always been played on the same surface, is played on grass. The Australian Open switched from grass to hard courts in 1988 and in its early years the French championship alternated between clay and sand/rubble courts. The US Open is the only major to have been played on three surfaces; it was played on grass from its inception until 1974, clay from 1975 until 1977 and hard courts since it moved from the West Side Tennis Club to the National Tennis Center in 1978. ITF uses the following classification for tennis court surface types: Clay courts Clay courts are made of crushed shale, stone or brick. The French Open is the only Grand Slam tournament to use clay courts. Clay courts slow down the ball and produce a high bounce in comparison to grass or hard courts. For this reason, the clay court takes away many of the advantages of big serves, which makes it hard for serve-based players to dominate on the surface. Clay courts are cheaper to construct than other types of tennis courts, but a clay surface costs more to maintain. Clay courts need to be rolled to preserve flatness. The clay's water content must be balanced; green clay courts generally require the courts to be sloped to allow water run-off. Clay courts are more common in Europe and Latin America than in North America, and tend to heavily favour baseline players. Historically for the Grand Slams clay courts have been used at the French Open since 1891 and the US Open from 1975 to 1977. Grass courts Grass courts are the fastest type of courts in common use. They consist of grass grown on very hard-packed soil, which adds additional variables: bounces depend on how healthy the grass is, how recently it has been mowed, and the wear and tear of recent play. Points are