So! Starting with the first section - the cylinders around arbitrary minor axes - you've done a pretty good job. You've been fastidious and patient in checking the alignment of your ellipses and marking out even the smallest of deviations, which definitely goes a long way to helping you improve and generally get more consistent results. One thing I did notice however has to do with the foreshortening on your cylinders.

It's normal to understand that foreshortening relates to the rate at which the scale of either end shifts smaller as we move from the end closer to the viewer to the end that's farther away. If this shift is more dramatic, it tells the viewer that the cylinder is longer. If the shift is more shallow, it tells the viewer that the cylinder is shorter.

This scale shift is not the only aspect of foreshortening, however. The shift in degree (where the far end is proportionally wider than the near end) is also an element of foreshortening. If the degree shift is more dramatic, and that far end gets much wider, this tells us that the object is longer, whereas if it's roughly the same width (just slightly wider), then it's going to be a shorter cylinder.

Because we have two separate properties to our foreshortening, we can end up with contradictions. Basically situations like 150, where the degree is fairly close but the scale shift is more dramatic tell us that the cylinder is both longer and shorter, depending on which aspect you look at.

So! Long story short - keep this in mind, so you can maintain consistency between these properties. It'll help you keep your cylinders, and objects in general, from feeling off.

Moving onto your cylinders in boxes, it's worth mentioning exactly what this exercise is about. While it helps a great deal in improving one's ability to construct specific cylinders that occupy a particular position and orientation in space, it's actually more about the boxes themselves. Just like how when doing the box challenge we draw extension lines so we can identify where our mistakes are, gradually working to reduce those mistakes and get better at intuitively constructing boxes that are more rectilinear, with lines converging more consistently to 3 set vanishing points, what we're doing here helps us to get better at drawing boxes with two opposing faces that are proportionally square.

The cylinder gives us additional lines whose alignments we can check against the vanishing points - if they fall in line, then this tells us that the ellipses on either end represent circles in 3D space - and therefore the planes that contain them represent squares in 3D space as well. Being able to eyeball these proportions naturally and intuitively is a useful part of developing one's general spatial awareness.

Looking over your set, it seems like you've largely only applied the original line extensions of the boxes themselves, and skipped extending your cylinder's minor axis and its contact points, which are explained here in the instructions for this challenge.

You attempted to do this a few times closer to the beginning of the set, but seem to have outright forgotten after the first page or two. This definitely impeded your progress with this challenge - while you definitely got better at constructing the cylinders themselves, this additional aspect of the challenge was neglected.

As such, before I mark this challenge as complete, I'm going to ask for you to draw an additional 30 cylinders in boxes, applying the line extensions as demonstrated in the notes.