Our signatures, God provides. This we see in a number of guises. Durer was working out proportions mathematically as was quite common in his day. Around this time others in Italy were trying to work out perspective with a range of techniques like golden geometry to take them to the golden section with the vanishing point, the God zone and other ways their bloodlines would allow them to see. Durer and other German bloodlines were concentrating on the chest cavity as though they needed to understand the measurements of God. Germans would have a different God zone. Our signature would nominate our bloodline. Your hands are a signature of your birthright and God gave us who we are.
