All in all you've done a pretty good job. Starting with your cylinders around arbitrary minor axis, you've done a great job of analyzing and identifying the correct minor axis of each of your ellipses. To start your margin of error was pretty small, which is great to see, and has steadily continued to improve throughout the set (although as you get closer to correct, the improvements naturally become less and less significant).

There are a couple quick things I wanted to call out however:

• In the cylinders, we've got two distinct shifts between the ellipses on either end. First you've got the obvious shift in scale that we're used to when it comes to foreshortening. End farther away from the viewer is going to be smaller in scale than the end that's closer. Secondly, we have the shift in degree - farther end is always at least a little wider than the end closer to the viewer. The key thing to keep in mind here is that both shifts are proportional to one another, and both are governed by the amount of foreshortening being applied. A significant shift in either will suggest that the cylinder is longer, whereas a shallower shift in either will suggest that the cylinder is shorter. What this means is that you won't run into situations where there's a dramatic shift in scale, but a shallow shift in degree, or vice versa. So if we look at cylinders like #33, something about it feels a little off (because there's a more dramatic shift in scale than there is in degree).

• Overall, I'd definitely recommend in the future allowing yourself to give each cylinder more room on the page, and perhaps cramming fewer onto a single page than you have here. You've still done a pretty good job of engaging your whole arm when drawing, and demonstrating solid spatial skills, but in general it's always a good idea to give your brain plenty of room to think through these spatial problems. Forcing things to be too small can definitely be a hindrance and an obstacle.

Moving onto your cylinders in boxes, again you've largely done a good job and have shown steady improvement in the specific area this exercise is meant to focus upon. Specifically, this is actually more about the boxes than the cylinders. Just like how we use the line extensions in the box challenge to give students something more concrete and clear to bring in line, getting them to converge more consistently towards the vanishing point, and in turn getting a better sense of how to intuitively construct boxes that are correct in perspective, adding the cylinder and its own lines helps build an intuitive grasp of something else.

Given that the lines (the minor axis, the contact points) line up with the vanishing points of the containing box only when the ellipses actually represent circles in 3D space relative to the given definition of space, then it stands to reason that this will also only happen if the plane containing the ellipses are proportionally square. So, by checking these additional lines, and gradually shifting our approach to get them to align together more effectively, we slowly develop our ability to intuitively draw boxes that have a pair of opposite faces that are actually square, rather than just rectangular. This isn't going all the way to drawing proper cubes, but it does end up being quite useful as we get into constructing more hard-surface, geometric objects.

I did notice one little hiccup towards the beginning - in a few cases you were extending your sets of parallel lines in the wrong direction, like with 13, 16, 17, and so on - but that issue became less prevalent and ultimately disappeared through the rest of the set.

All in all, your work is looking good. I'll go ahead and mark this challenge as complete.