Just realised I’ve missed a vital detail on my post, it’s 12mm wide + or – 0.1mm.
Barion Heart Transplant has to be 12mm wide at the point where facets P8, P9, P14, G5 and G6 meet. The instructions have you cutting the P facets first and the intersection where they meet is out in space and can’t be accurately measured from one side of the stone to the other. Plus your restricted as to how deep you can cut them because you have already cut P1 and P2. Way beyond my limited mental capacity to figure it out so changed the cutting sequence.