In matching up my model with this high resolution image, I noticed a couple of things right off the bat.
The fingers are too thin at the tips. I had some advice from an acquaintance online some years back that all the fingers (but not the thumb) were square in cross-section. The fingers were all made out of a single shape with the same top and bottom measurements, and then cut and angled to fit in their final positions. Once I learned that, it was relatively easy to place the fingers in their correct positions. The first ones I tried weren't square and were a huge pain to try to edit. Making them square immediately made them look right.
The second thing is that the wrist and the base are too thin side to side. Which is a good thing, because I have been trying to install a motor with which to rotate the hand, and a slip ring through which to light it, and the available room has made that a bit challenging.
The arm and the wrist are too simple. I made them as perfectly flat, and three-sided on the bottom, six on the top. The real arm has two facets per side, not just one. The top of the black base gets narrower where the two facet corners touch it. The wrist has two facets that come to a point at the top, leaving it hexagonal in shape, so I believe I got that right.
My black base is a triangle, but that isn't quite right. The angles of the top of the real base facing away from the camera, don't meet up as they do on my computer model. By extending the lines I came up with a theoretical shape in yellow where the base sticks out in back about half as much as in front. That was making me rethink the entire base as a 4-sided shape, not 3. Then I noticed the shadow in the original photo: if the base and the arm did stick out as far as I extrapolated they might, then the shadow on the ground would probably be cast on the legs of the man on the right. Since the shadow doesn't do that, in fact it looks like it's coming right at the edge of the black base, I'm thinking the base is actually a five-sided shape, similar to Superman's shield. At least, that's the direction I'm going to take it. I'm also going to assume that the rear face of the arm, like the left and right sides, has two facets that come to a shallow angle in the center.
Speaking of shots of the hand from the back, I had assumed that there existed some shots from the other side of the arm. But in reviewing all the old and new stills I have collected, I realize that I have only ever seen the statue base from the angle pictured. The closest I have seen to a rear shot are pictures from the top of the escalator shooting down, and there are always people on the escalator blocking the view of the base. Anyone else seen one?