Starting with your cylinders around arbitrary minor axes, your work here is for the most part fairly well done. You're conscientious and consistent in checking the alignment of your ellipses, and their "true" minor axes, and I'm pleased to see that you included a variety of rates of foreshortening, from cylinders that had a shallower shift from one end to the other, as well as many that had a more dramatic shift.

In looking at these in particular, I did notice an issue that come up very infrequently, but that I do try to look out for. This is the case with all forms, but it is particularly easy to identify in cylinders - foreshortening is represented in two different ways. First we have the standard shift in scale, where the far end ellipse is smaller than the closer end. Then we also have the shift in degree, where the far end gets wider than the closer end, proportionally speaking. Both of these represent how much foreshortening there is, and therefore how much space there is between the two ends relative to other things in the same scene.

What this means is that if the shift in one is dramatic, so too should the shift in the other. If the shift in the scale is significant, we should also be seeing the far end getting much wider. That's why, looking at cylinder 147, we actually see a contradiction. The shift in scale tells us there's lots of space between the ends, that the cylinder is quite long. But the shift in degree tells us that the two ends are actually quite close together, because the shift from one end to the other is minimal in this regard. And so, we end up with a contradiction - something the viewer will pick up on, even if they don't know specifically what looks 'off'.

Something to keep in mind!

The only other thing I wanted to address here was just the fact that your ellipses do tend to be kind of loose, so that's something you'll want to continue working on. Be sure to apply the ghosting method here, and draw from your shoulder to avoid the kind of variances that can result in a looser ellipse.

Moving onto your cylinders in boxes, you've done a great job. As discussed in the notes, this exercise is all about the boxes - specifically training the students' instincts to better construct boxes that feature two opposite faces which are square in proportion. By checking these additional line extensions (those of the ellipses), and identifying how far off they are from aligning towards the box's own vanishing points, we're able to test how far off those ellipses are from representing actual circles in 3D space - and therefore how far off the faces that enclose them are from being proper squares in 3D space. As we make adjustments to bring those more in line, we improve our ability to eyeball those proportions, something that will be very useful in lesson 6.

To that point, I think you've developed that skill quite nicely, and your estimated proportions by the end are very believably square. Well done.

I'll go ahead and mark this challenge as complete, so keep up the good work.