From crochet.about.com - Crocheting in the Round
Crocheting in the Round - Basics For Increasing
When crocheting circles (rounds), what can you do to keep your crocheted piece from buckling in the middle?
Increases in the pattern keep the work lying flat. Most patterns are written with the correct amount of increases and there is no problem. If buckling does occur, however, try adding more (or less, if needed) increases in your rounds until this corrects the problem.
Common Increasing Formula
Increases start on the second round. This example uses double crochet stitches: An increase is made by making 2 dc in a same stitch. On the second round, work 2 dc in every dc around the circle. On round 3, make an increase on every other stitch - in other words, (dc in next dc, 2 dc in next dc) around.
These Southwestern Duo Potholder Patterns are an example of using rounds with increases.
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