What is 'double in, double out?'published at 20:05 BST
Humphries v Littler (20:15 BST)
Unlike most darts tournaments, the World Grand Prix uses a 'double in, double out' format, presenting a big twist to the gameplay.
This means that a player must start all legs on a double, rather than on any scoring zone on the board.
The use of 'double in, double out' has been in use in the World Grand Prix since its inaugural year in 1998.