Not a direct answer to the question posed, so I’ll tiny-type it. I simply measure the length between my last and middle knuckle of my index finger on my left hand. I am at the age where the bone will not grow anymore, so the measurement will stay accurate. I simply remember the number, but I suppose you could tattoo the measurement down so you wouldn’t forget. That way, you would not have to worry about sagging/stretching skin altering your measuring tool.