The index dots are between the arrow and the line. They’re set to assist play angles.
What’s an Angle?
Angles are if the ball is discharged in the arrow over one board in the line and also a board. Since the two board amounts are somewhat distinct, As an instance if a bowler releases the ball above board 12 and rolls it it is an angle.
After a Trail
Considering that the bowler knows where the ball will cross in the arrow along with the index dots, the bowler can envision. Each bowler can correct the space they originally seem (nearer or further ) to adapt exactly what works best for them.