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The increase rounds occur every 8 rounds. So work 7 rounds without any increase and then on the 8th round, increase one stitch at the beginning and on at the end of the round. Work these new stitches into the k4p4 pattern on the next round. You'll be repeating the 8 rounds 0 times or until you have 68sts.
Increase Rnd: Kf&b, knit to last st, kf&b - 2 sts increased. Work increased sts into the k4, p4 rib pattern as they become available, changing to the medium length circular needle if there are too many sts to fit comfortably on the shortes needle. work 7 rnds even. Repeat the last 8 rnds 9 times - 68 sts. Work even until piece measures 18.5 in from beginning. On the next round, place the last 8 sts just worked on a stitch holder, removing the marker for end of rnd from the middle of these sts, work in pattern to end - 60 sts on needle. break yarn.