In professional bowling, the United States Bowling Congress has very specific measurements for the bowling balls players can legally use. Finger weight refers to the center of gravity of the ball relative to the finger holes. Extra finger weight will let the ball travel further with more power. To determine subtle changes in a ball's center of gravity, you need a special tool called a dodo scale, which measures finger weight in increments of an ounce. The USBC allows for no more than an ounce in finger weight--any more, and the ball is not regulation.
Position your dodo scale so that your weigher, the circular ring where you'll set the ball, is facing to the left. There are two beams to the right of the weigher that measure both the weight and balance of the ball at the same time. The balance beam should be in front and the weigh beam should be in the back.
Place your ball in the dodo scale so that the holes are centered and facing directly toward the ceiling. If the holes are not upright, the scale won't properly measure finger or thumb weight.
Rotate your ball in the scale so that the two finger holes are closer to the beams of the scale (toward the right) and the thumb hole is further from the beams (toward the left). An imaginary line drawn between the two finger holes should be in centered horizontally on the dodo scale. An imaginary line between the finger and thumb holes should split the ball vertically in half on the scale, and the point where the two lines meets should be the topmost point on the ball.
Set the poise, or the movable measuring tab, on the balance beam at zero. Then move the poise on the weight beam so that the ball is balanced. You will be able to easily see when the ball is balanced because the scale will be level.
Rotate the ball carefully so that the thumb hole is now in the finger holes position and vice versa. Essentially, you're comparing the weight of the thumb side of the ball to that of the finger side. If you have to move the poise on the balance beam to the right, that means you have a positive finger weight on your ball. Move the poise until the scale is balanced again. The difference must be no more than one ounce for the ball to be regulation weighted. If you have to move the poise to the left, that means you have positive thumb weight, which also must measure at one ounce or less.