Nicely done! Starting with your cylinders around arbitrary minor axes, you've done a good job of checking your ellipse alignments conscientiously, and I can see a clear sign that your margin of error, and the frequency of those errors, has diminished quite a bit with more of the ellipses aligning more correctly to your intended minor axis towards the end of the challenge than towards the beginning.

I'm also pleased to see that you incorporated a wide range of rates of foreshortening, rather than sticking to the same one. This helps me look out for certain issues that are common amongst students at this stage. I caught a couple instances of this issue in your work, but overall it does appear that you were constructing these well.

The issue to which I'm referring has to do with keeping the rate of foreshortening - and the various manifestations of it - consistent. Foreshortening shows up in our cylinders in two "shifts". There's the shift in the overall scale of the ellipses, where the closer end is larger and the farther end is smaller. Then there's the shift in degree, where the closer end is narrower, and the farther end is wider. The key is to make sure that at no point is there a dramatic shift in one, but a more minimal shift in the other.

One such case I was able to find was cylinder 141 - here we can see that the scale shift is quite notable, but the ellipses' degrees are roughly the same. I'm going to write this one off as a fluke however - there aren't really many other such cases throughout your work, so overall I'm confident that this is something you grasped on an intuitive level, and with it explained here, it should be something you can maintain more intentionally as well, moving forward.

Continuing onto your cylinders in boxes, I think you've done quite well here as well. In applying your line extensions just as fastidiously as with the first section, you've worked well towards developing your intuitive grasp of how to construct boxes that feature two opposite faces which are proportionally square. That is in essence the focus of this exercise - we take the line extensions from the box challenge, and add ellipses to them, which have their own lines (the minor axis and two contact point lines).

By checking the ellipses' lines against the box's own vanishing points, we can find how far off we were from those ellipses representing circles in 3D space. After all, if an ellipse's 3 lines converge towards the vanishing points of the box upon which it was drawn, then it would represent a proper circle, in 3D space, on one of those faces. And if it does, then that face enclosing it would too represent a square in 3D space. As we do our line extensions and adjust our approach to bring those extensions more in line with one another, we inherently train our brain to become biased towards these key proportions.

As a whole, I can see that your estimation of those proportions has come along quite nicely, and that this should be quite beneficial throughout the next lesson. So! I'll go ahead and mark this challenge as complete. Keep up the good work.