Why use your hand when you can read the numbers off the periscope. Makesanosensa. It's like counting the legs in a herd of cattle and dividing by four to count the cows..
We don't measure angles in mils and neither did Kretschmer so I'm calling bull on this one too. If you really want to learn to use your hand to measure angles then read a book an amateur astronomy. I've been doing it for 30 years and the method has no resemblance to this monstrosity you propose.
Not one sub skipper on Subsim has ever measured an angle in mils and never will. By the way, your hand is NOT spread out as pic 1 shows. Not even close. And you ignore the most important part of the instructions, making your measurements totally worthless. You propose a classic misunderstanding of what you have read. Please don't try to lead our Subsim community astray with your fallacies.