N.B.: there are copious errata for Hip Knit Hats.

In fact, I do not think the cast on numbers are even correct, although there are no corrections for them. Many of the hats indicate casting on 12, then doing *k1,m1* across to give 18 sts.

In MY mathematical universe, doing *k1, m1* across over 12 sts gives 24 sts, not 18. So either you're supposed to only cast on 9 sts, or you're supposed to somehow skip over some of the sts in the row. Or skip the row with 18 and go straight to 24. ALL of the hats in the chapter are like that so I can't even look at another pattern for clarification.

I've just fudged it - figuring there need to be six increase points and taking it from there.

(Do note: the author also provides a free hat pattern on her website to reward people with their "forebearance" with the errata.)