Jumping right in with your cylinders around arbitrary minor axes, your work here is really well done. Your linework is all very confident, which helps to keep your ellipses smooth and evenly shaped, while also keeping those side edges precision-straight, to a degree that I think is quite impressive. You are also doing a great job of checking your ellipses' minor axes, catching both more obvious discrepancies as well as those that can be harder to identify if we don't pay attention - something that can lead to plateauing of one's growth with this sort of thing, which I'm glad to see you're doing a great job of avoiding.

Continuing onto your cylinders in boxes, your work here is for the most part well done, although I do have a suggestion or two to offer in how to continue getting the most out of this exercise, and avoiding certain pitfalls that may be present in your current approach.

This exercise is really all about helping develop students' understanding of how to construct boxes which feature two opposite faces which are proportionally square, regardless of how the form is oriented in space. We do this not by memorizing every possible configuration, but rather by continuing to develop your subconscious understanding of space through repetition, and through analysis (by way of the line extensions).

Where the box challenge's line extensions helped to develop a stronger sense of how to achieve more consistent convergences in our lines, here we add three more lines for each ellipse: the minor axis, and the two contact point lines. In checking how far off these are from converging towards the box's own vanishing points, we can see how far off we were from having the ellipse represent a circle in 3D space, and in turn how far off we were from having the plane that encloses it from representing a square.

For the most part, you are applying those line extensions correctly, save one area: the minor axis. From what I'm seeing, it appears that you're extending the minor axis line you'd drawn when planning the ellipses, rather than actually checking the minor axis for each ellipse separately. What we want is for each ellipse to have all three of those line extensions I'd mentioned above: one minor axis, two contact point lines, per ellipse. These line extensions describe the ellipses, which in turn describe the plane in which they've been set. If we miss out on one of them, then it becomes quite easy for errors to hide there - kind of like only checking two out of the four corners of a room with a flashlight when inspecting for monsters.

So for example, if we look here at 231, we can see that the actual minor axes are off by a fair bit more than what your line extensions showed. The closer ellipse isn't too bad, but that rear ellipse is starting to align more to an entirely different axis, than the one it was meant to - and that could have gone unnoticed in your analysis.

Lastly, I also noticed that 195 had lines extended in the wrong direction (you seemed to extend one set to the right instead of the left, it seems like you may have decided this by focusing on which direction those lines were converging in. Unfortunately your lines were actually diverging as they moved away from the viewer, which is why relying on the direction of the convergence isn't always reliable.

All in all, you're headed in the right direction, so just be sure to keep what I've said here in mind when practicing these in your warmups. I'll go ahead and mark the challenge as complete.