Here are the stitches/techniques you should know for each rating:
slipstitch (sl st) chain (ch) double crochet (dc) increase (working two double crochets into same stitch), decrease - double crochet two together (dc2tog) basic sewing |
stitches for rating 1 half treble crochet (htr) treble crochet (tr) |
stitches for rating 2 double treble crochet (dtr) triple treble crochet (trtr) |
stitches for rating 3 using only front loops using only back loops picot (p) awkward or fiddly sections in pattern |
stitches for rating 4 cluster (cl) popcorn (pc) complex assembly of pieces of the pattern (eg for a toy) |