Do you have any calibrated body parts? Sounds weird but I know my pointer fingernail is 1/2 inch, first pointer finger joint is 1 inch, 2nd joint is 2 inch, finger tip to knuckle is 4 inch, extended thumb tip to pointer finger tip is 7 inches and spread thumb tip to pinky tip is 9 inches. With a combination of these between two hands I can get pretty accurate measurements pretty quickly.