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Well, that's up to you...core center is were the thinnest part of the side cut is and where the highest point of the ski vertically is, and where the weighted center is. True center is obviously measured center. True center will have lower swing weight and be more balanced on rails, while core center will carve and ride better (not that you can't carve and ride at true center - it's just that the ski is made to carve at core center).