The rocks have been reorganized to get similar rocks grouped together. Each set has rocks of more or less comparable speed, and gradually increase speed as you go through the set. Set A is comprised of the slowest rocks, with some really bad ones at the front end. C has rocks that are just below average speed, but should be fairly consistent. B rocks are as consistent as C, and perhaps a hair faster. D rocks are the fastest of the 4 non-ceramic sets, with the skips stones really flying.