This is a canvaswork filling stitch consisting of diagonally offset triangles.
For the first unit, make a tent stitch across one canvas intersection.
Below it make a stitch across two intersections, then three, then four.
Repeat this sequence of stitches over one, two, three and four canvas intersections in a diagonal row from top left to bottom right.
Work the next row of triangles in reverse, so that they fit into the gaps of the first row. The smallest stitch of one row should always be next to the largest stitch of the following row.
Structure of stitch
This stitch is worked in diagonal rows of triangular units.
Rachel Doyle, RSN Essential Stitch Guides: Canvaswork (2013) , p.70
Mary Thomas’s Dictionary of Embroidery Stitches (1934) , p.149–50