Crochet in the round
Joined rounds close with a slip stitch; continuous rounds spiral and need a first-stitch marker.
Work the technique
For continuous US sc rounds, place a marker in stitch 1 and move it each round. For a joined round, close in the specified first stitch, then make the next height chain.
Try it on a sample
Make a flat sc circle: 6 in a ring, then 12, 18, 24 and 30 by adding six evenly spaced increases per round.
Check and recover
A cupped circle needs more circumference for the height; a ruffled circle has too much. Gauge and stitch height determine whether six increases per round lie flat.