Last month on my trip to New York I was able to see the original of this drawing in the study room of the Met. The mere 40 minutes I was able to look at the original drawing (and the fact that I was a bit overwhelmed being in the presence of it) made it impossible to do a satisfactory study of it.
So I bought a reproduction at the Met gift shop, and this week I did this study of it. I spent about 8 hours on this.
I am so amazed by the organized matrix of systems that make up a human being. I say "matrix" because every part is interrelated to every other part, like a grid. To put any landmark in the wrong position skews every other landmark in the drawing.
And of course Michaelangelo designs his drawing to illustrate these relationships. Copying his drawing is like watching a chess player think.
For fun I've diagrammed some of the relationships I found:
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You can see how the fast sketch (in red) has the left arm too far over to the left. I did the same thing on the longer sketch, but later realized my mistake and adjusted it back over to the right, fairly far into the drawing.
I think I did that twice because I see the head as positioned between the two hands, so I unconsciously tried to center it between the two hands. In reality, it is much closer to the left hand.