Multiple of 3
This stitch looks best using contrasting wool.
Abbreviations: C: colour; sl 1: slip 1; k: knit; rep: repeat; p: purl
Row 1: C1: *sl 1 purlwise; k2* rep from * to * until end
Row 2: C1: p
Row 3: C2: *k2; sl 1 purlwise* rep from * to * until end
Row 4: C2: p
These 4 Rows form the pattern. Repeat as required.