See someone on the website has queried the X and Y markings.
I'm beginning to think that the measuring and geometry bit are not her strong point. I have never done quilting before, but if I wanted to design a block like this, I would draw it inside the finished measurements, cut out the pieces, having coloured them, and then draw a seam allowance around each. What could be easier? Correct me if I have missed something, please, you experts.