With absolutely no clue, I take a medium ball out of the bag and play straight up 10. When the ball comes back, oil rings and their size and "juicyness) tell me a lot about the pattern, as well as the ball reaction.
From there I adjust just my feet and target, when I see that the ball finishes well, or I switch the ball according to the reaction I saw (stronger/weaker coverstock). Works quite well, and if I am lucky I can find a competitive line within 3-5 shots. System fails a bit through myself, since I need the warmup shot in league and tournament and am hardly loose enough to adjust my game for the foreign lane. Getting both objectives at once is quite a challenge, but the "down-10-and-adjust" method is what I practice in this situation.
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DizzyFugu - Reporting from Germany
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