Being used to metric system, I didn’t think about how centimetres translate into my 60” wide fashion fabric, so I went on measuring one meter along the seam joining two pieces of muslin together (my lengthwise grain). I divided that one meter into twice 50cm and drew a line along the crosswise grain (folding fabric in half helps)
I have already figured out the problem with instructions and measured twice 50 cm to the left and twice to the right. (How stupid, I didn’t add up, because then I would know that I am ending up with 2m width – 50cm wider than my fashion fabric)
Note, how the diagonals cross the rectangle forming four equally sided (15" for each side) triangles. Now, they mark the true bias.