Cast on the relevant number of stitches for your square.
Row 1) Knit all stitches.
Row 2) Knit 1, Purl 1 Repeat this to the end of the row.
Repeat rows 1 & 2 until your square is the correct size.
Broken rib creates a flat rib on one side & moss stitch on the other.
It is one of my favourite stitches.