Hi Jorr19,
The RG listed is what is called the Low RG. Basically, when determining the RG, tests are run in a cradle on an x,y,and z axis. Each axis has it's own RG measurement, and the lowest RG rating is the one that we use for our advertising. For example, a ball may calculate out to have the following:
x - 2.540"
y - 2.573"
z - 2.585"
In this case, we would put in our advertisements LOW RG - 2.54". You can also see from the measurements that the Differential (aka differential radius of gyration) is .045" This measurement is determined by taking the difference between the high and low RG measurements.
RG measurements tell you a little bit about how the weight is distributed in the ball. A low RG ball means that the average weight distribution is closer to the center of the ball. A high RG ball means that the weight is more towards the outside of the ball. These measurements are different on each axis, and the greater the difference, the higher the differential.
Hope this helps,
Jason Wonders
Visionary Bowling Products