Abstract: A computer device for assisting spot bowlers to determine starting position and direction in which to bowl a ball to collide with a predetermined pin or group of pins, comprising two coextensive, rectangular members. On one member, a representation of a bowling lane with appropriate markings is obversely displayed. The other member is transparent and contains a bowling ball indicator that is concentric with the five-pin location spot when the two members are aligned. The invention is calibrated by aligning the two members and for a strike ball tracing a straight line from the starting position of the proper foot to the target over which the ball passes on the transparent member.