It's doing the shaping by short rows where you don't knit all the stitches across every time.
So do 2 rows on all the stitches, then turn and knit 52 sts, turn and knit back over (same as 'on') those stitches. Next row, k 44, turn and knit back over the same sts. On the next row you work that sequence again - knit all sts for 2 rows, knit 52 sts for 2 rows, k44 for 2 rows. The size of it will be determined by how many rows you do, not by the number of stitches.
sue- knitting heretic