Really, really nice work! Overall you've demonstrated a great deal of patience and care not only in each and every mark you put down (taking the time to apply the ghosting method consistently), but also in applying the line extensions and minor axis corrections.

Before I get further into the critique though, I did notice that your scans, though they're generally all of decent quality, do have a very high contrast setting. This is likely your scanner's doing - often students will use the 'drawing' presets on their scanner because it seems like the obvious choice, but it has this higher contrast result. In the future, always opt to use photo presets, which capture the nuance of your linework more accurately.

Back to your critique - starting with the cylinders around an arbitrary minor axis, you've definitely got exceptional grasp of drawing ellipses that are generally tight and evenly shaped, and the control with which you do so is keeping them relatively correct against their given minor axis. While there are some slight deviations here and there (which you captured yourself), the margin of error is quite small and not generally noticeable until we get up close.

One that did jump out at me was cylinder #50, where the ellipses themselves have a very wide degree (suggesting that they're facing the viewer). There is considerable distance on the page between the ellipses however, which suggests that the distance between those ellipses in 3D space is pretty significant, even though we're not getting the other effects of perspective on that farther end. As such, this one feels off (though the viewer may not always be able to determine why).

One other point to mention is similar - if you look at a cylinder like 102, you'll see that the scale of the near/far end has the farther end being a little smaller (which according to perspective is correct). What we're not seeing however is a corresponding shift in the degree of that far ellipse, which is another aspect of perspective. If we see the far end get smaller in scale, then we should also see the degree get wider correspondingly. I did notice that for the most part your cylinders didn't include a lot of dramatic foreshortening, so in the future I'd definitely practice more of that to ensure that you can tackle either scenario.

Moving onto your cylinders in boxes, while this exercise pushes you to get familiar with placing ellipses inside of planes and dealing with all of the criteria and rules for having those ellipses represent a circle in 3D space, what this exercise actually does most of all is develop a student's ability to draw boxes in 3D space that have faces that are proportionally square when compared against other constants within the scene. This is because of the simple reason that if your plane isn't "square", then an ellipse you place within it won't represent a circle. To this end, you've demonstrated a great deal of growth in your comfort with constructing such boxes. By the end, you were falling within the margin of error that wouldn't be easy to spot with the naked eye.

All in all, you've done a great job throughout this challenge. I'll go ahead and mark it as complete. Keep up the good work.