I believe there is a bit of errata in the Turtle Check Pattern -- missing rows 18, 19 and 20. Which I believe should be:
Row 18: work as row 2
Row 19: work as row 1
Row 20: work as row 2
in other words -- work sts as they appear (knit the knits and purl the purls)

The pattern calls for 4 skeins at 220 yards/skein.