Pocket billiards, often known as pool, is a billiards game popular in the United States and Canada that is played on a rectangular table with six pockets using a white cue ball and 15 sequentially numbered colored balls (one at each corner and one at the midpoints of both longer sides). The object is to get points by sinking balls using shots from a pool cue. 8-ball is one of the most difficult games to master because you have to be able to hit every ball perfectly or you will lose quickly. It is more difficult than 9-ball because you only get one chance for each shot. You can improve your game by practicing more games, reading about history of pool, and playing against computer players. The modern game of pool was developed in the late 19th century in England by George Thomas. He added several rules to the previously existing game of bragpool, including limiting players to one shot per turn, requiring players to stand behind their chairs when making shots, and prohibiting hitting the ball out of the playing field. These rules made play safer and eliminated tactics used by braggarts to show off their skill. Today, these are the only rules used in 8-ball pool. Before becoming popular in North America, English billiards used different colors of balls to indicate which player was going next.