Because as Anglo has stated that when you use a 20* layout it's going to place your rg/mb past your val in most cases, which creates early revs/earlier roll. The lower degree(10* or 20*) you use for your drill angle the earlier the ball will roll and the higher degree(70* or 90*) the later the ball revs. The lower deg* you use for the val angle the closer to your val the pin will be and the higher your val angle the farther away from the val the pin will be placed. Remember using the dual angle layout, the lower the combined number the earlier the ball will roll and the higher the combined numbers the later. Just my $.02, Bruce
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"Train a child up in the way he should go and when he is old he will "BOWL UP A STORM WITH THE BIG B AND YOU WILL BE MO-RICH" and not turn from it."