When playing games of pool, it is frequently important to know where an object or cue ball struck with center ball will travel after contacting the rails. As a players aid, diamonds are inscribed at symmetrical locations around the table.
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A good player will use these marks as a reference for determining the outcome of a shot.
A few systems have been developed that make it possible to calculate, with the use of simple formulae, the position of ball contact with a rail based on the two diamonds lined up in the direction of the the ball when it is struck.