The dots on the approach are markers to aid the bowler to find a consistant
starting spot. These pictures show two different starting places.
The picture on the left shows the bowler's right foot on the board that also has
the centre dot. This centre dot is in a direct line with the centre arrow
and the head pin. The picture on the right shows a starting position that
is close to the original but not quite the same. The bowler has moved to
her left one board and is now on the board next to the centre dot.
Bowlers establish a 'home' starting position for a strike ball, a corner pin
pick and for each 3-2 pin side. This builds consistency. A bowler
with a very straight ball will stand very close to the centre dot. A
bowler whose ball moves more on the lane will stand further away from the centre
dot to adjust for the break (movement) of the ball.