Work the first row from left to right. Bring the needle up and make a diagonal stitch from bottom left to top right over two threads.
Come up to the left over two threads and make a long-arm of the cross slanting down as shown in the picture (two threads down and four stitches across).
Come up to two threads to the left and take your needle down two threads to the right and two threads up to make a diagonal stitch. Your diagonal stitch should be at the same angle as your first stitch.
Come up to the left over two threads where the first diagonal stitch went in, and make a long-arm cross slanting down.
Work the second row from right to left.
First, bring your needle up two threads down from the bottom right point of your previous row. Count two threads up and two left to make a diagonal stitch.
Come up two threads to the right, and make a long-arm cross slanting down in the opposite direction (two threads down and four threads across).
Structure of stitch
Identifying Greek stitch
Greek stitch forms lines of back stitch on the reverse side.
Mary Thomas’s Dictionary of Embroidery Stitches (1934) , p.110
Jennifer Campbell, Ann-Marie Bakewell, Guide to Embroidery Stitches (2004)