This is Bob's 27, a great practice
routine developed by Bob Anderson to help you work on your
doubles. Starting off with 27 points, you go round the board
throwing three darts at each double from 1 to 20 in consecutive
order, finishing on the Bull. Every double hit earns you the
double's score and is added to your total, e.g. 2 hits on
Double 2 earns you 8 points. Miss a double with all three darts,
and the value of the double gets substracted from the total,
e.g. 3 misses on double 6 and 12 points are substracted from
your points. Try and finish the board but once you're down to
zero or less the game is over.