Ah ha, an interested student,
The United States Bowling Congress defines certain static weight limits that our bowling balls must comply with. Those weights are:
For a ball weighing 10 pounds or more:
(a) Not more than three ounces difference between the top of ball (finger hole side)and the bottom (solid side opposite finger holes).
(b) Not more than one ounce difference between the sides to the right and left of
the finger holes or between the sides in front and back of the finger holes.
The weight limit in remark (a) is known as top weight. We refer to the other weights as side weight (positive or negative) and finger/thumb weight. This rule implies that we are weighing the difference between the two ball halves from 3 different positions.
The inherent problem with the Kaufman scale is that it does not weigh through the center of the bowling ball. The ball is held in the ring to the left side of the scale. There are two bearings that the scale pivots on, located just to the right of the bowling ball. The line that passes through these two bearings is in fact parallel to the line described in the static weight rule above (whether it be side, top/bottom, or finger/thumb). But because this line that passes through the pivot point does not pass through the center of the bowling ball, you are not getting a true representation of the difference between the two ball halves. You are weighing an object on the end of a pendulum with weights suspended at an appropriate distance in the opposite direction.
This difference or error margin increases as multiple densities and pieces of material are present inside the bowling ball. The scale is not able to adjust for different positions and manipulations of core design. It is pre-calibrated with a particular set of balls and is designed to perform within a certain range.
Now don't get me wrong. I'm not slamming the Kaufman Scale or anything. In fact, I think it's a great scale. It's obviously the industry standard, and pictures of it even appear in the equipment specifications manual. What I find to be comical is that we have a rule in our USBC rulebook that virtually none of us can follow, due to the lack of a properly designed scale. In fact, for decades your bowling balls have been weighed at the ABC/USBC tournament on a Kaufman Scale, as it is the accepted standard.
But it's important to realize that the Kaufman scale is not weighing EXACTLY what the rule book defines as our static weights. Without weighing exactly through the center of the ball, it is impossible to weigh the ball as definied in the rulebook.
I'm working on some qualitative data that I'll post for you later today. I've been testing balls on different scales for years, and this subject has come up several times in the design phase of other new products. Hopefully you can conceptually see how not weighing on a pivot point that travels through the center of the ball will not give you the EXACT results that you are trying to find.
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Jeff Ussery
Powerhouse Training Clinics
www.proshoptraining.com
