on drilling layouts, what does each measurement determine? what will email@example.com do more or less of firstname.lastname@example.org
We need to qualify more specifically what type of ball/core we're talking about with these drillings.
For an asymmetrical-cored ball (Cruel, Raptor), the first number denotes the amount of length the ball can produce (depending on the surface, of course), or more specifically, controlling the amount of time the core will take to make the first transition. The second degree measurement more or less describes the type of shape at the breakpoint the ball can produce, or more specifically how quickly the second transition will take place, again, depending on the surface prep of the ball. A smaller second degree number (also called the VAL angle) will create a quicker response to friction, or a sharper breakpoint shape. For asymmetrical balls, the pin-to-PAP measurement (the inches, either 3.5 or 4.5 in the example above) is rather inconsequential because asyms have similar amount of track flare in the pin-to-PAP zone of 3.5 to roughly 6".
However, for symmetric core balls (all Sigma cored balls, Quadfire cores, Gear cores, Thrust cores and Recon cores), the first measurement (55 degrees in the above example) is inconsequential. You can control track flare (differential) by changing the pin-to-pap distance. Maximum flare occurs when the core is at a 45* angle to the axis, most times expressed as a distance of 3 3/8" pin to PAP. I tend to doubt that this is an absolute for everyone. (Just read my rant later on the "Rico" drilling.)
As all symmetric cored balls become asymmetric when you put holes in them, the second measurement (the VAL angle) can also help you shape the breakpoint response, like in the asymmetric balls explanation above.
If you were to search the boards here, JustinWi has posted several very informative and interesting (to bowling geeks like me) articles, links and diagrams to help explain the art of laying out symmetric balls.
Hope this helps to shed some light for you!