Nicely done! You've done a solid job here, and have demonstrated a great deal of patience and care with each and every cylinder you've drawn. Each ellipse is drawn confidently, and you've managed to keep them quite tight and concise, which shows that your overall control and accuracy has definitely grown a great deal. You've also been quite fastidious in going through and applying your corrections/analysis to each and every cylinder.

Through the first section, it's very nice to see that you didn't really get overly focused on the fact that there was a minor axis you'd drawn that was already there, and instead identified the "true" minor axis even when it was just a couple of degrees off. This is the kind of attention to detail that promotes growth even when we're pretty close to nailing things. That's what keeps us from plateauing entirely.

One thing I look for throughout the first section is whether or not the student has picked up on the relationship between the shift in scale between the far and near ends of the cylinder, and the shift in degree between them. It's not something I explain explicitly in the notes, as for now I'm leaving the student to come to this conclusion themselves. It is the fact that both of these are facets of foreshortening - as that far end gets farther and farther away, both the overall scale will get smaller, and the degree will get wider. This means that if one of these happens, then so too should the other - you'll never see a situation where the farther ellipse remains roughly the same degree, but the scale itself shifts a great deal. For the most part you've held to this rule, but I do see a small handful of cylinders - mainly those where you've introduced more foreshortening - where you shift the scale a lot, but don't do the same to the degree. Keep that in mind for the future.

Jumping forward to your cylinders in boxes, these are all very well done. You're not only demonstrating a strong capacity to construct cylinders inside of pre-set boxes (which will help you in the future when you need to place a cylinder within a specific orientation and location), but you've also improved in your ability to draw boxes that are themselves proportionally square. That is, with two opposing faces that are square rather than rectangular. This is one of the key purposes of this exercise as a whole - to help develop your judge of space and proportion. It works out this way because the error checking we do for our cylinders-in-boxes will turn up problems if the face itself is not square (since this would imply that any ellipse drawn within it would not be a circle in 3D space.

I have just one small qualm with how you've approached this exercise - and that's just how you've applied your line extensions. You've been very thorough, but I feel that avoiding drawing them directly over your linework makes it more difficult to see the relationship between the extension and the line being extended, which can make it all more difficult to process and learn from. I'd definitely recommend just drawing right over the existing lines in the future.

So! I'll go ahead and mark this challenge as complete. Keep up the good work.