This template is produced at Byrk.no in Norwegian, certified wood.
A small instruction is included.
Each groove is 1 cm apart, but with holes in between them so that you can draw lines 1 cm apart and then slide the template 0.5 cm to the side, check that the lines you drew are in the holes, and then draw new lines. Rotate the template 90 degrees and repeat, and you will have a 0.5 cm grid. You can also just draw 1 cm lines and estimate the half-centimeter when sewing.
This is practical for many clothing repairs, but especially for Hitomezashi ("one stitch" sashiko) where patterns are built up with a network of stitches constructed around grids of various kinds. Therefore, we also include a small hitomezashi instruction with all templates.
It is also practical just for simple rows of running stitch/basting stitch for mending or similar. You can, of course, also create larger or smaller grids than 0.5 cm if you wish by adjusting the number of lines you draw.
We have tested the template with various marking tools for textiles, so it works with both pencils and markers.
If what you are marking the fabric with is quite narrow, you can choose one side of each groove and make the lines against one side, and then just make sure that when you shift the template, the lines are not exactly in the middle of the holes, but slightly to the side, and then you draw new lines along the same edge as before. With pencils, it is important that you sharpen it frequently to reach the fabric you are drawing on.