The centre square is about 4cm
4cm is about 48threads (28ct linen)
Buttonhole Stitches were used to stitch the centre square.
（48 threads x 48 threads）
There are three triangles at the base of each pyramid
（48 threads / 3 triangles = 16 threads）
Mark the tip of each triangle.
A waste knot on the right hand side
Start the first stitch from the left hand side
Here is the link : How to do Hedebo Embroidery
Make sure you catch the thread on the other side of the fabric
When you reach the last stitch of the row
Whip back to the first stitch of the row
First triangle is finished
Whip down to the base of the triangle
Continue to the next one.....