Jumping right in with your cylinders around arbitrary minor axes, your work here is looking quite solid. Your linework is confident and well controlled, which shows that you're making effective use of the principles behind the ghosting method to produce smooth lines and evenly shaped ellipses, and I'm pleased to see that you're quite fastidious with your error analysis, where you've taken great care to check the true alignment of each ellipse. As we get closer to being more consistently correct, it's easy to fall into the trap of just not looking that closely and assuming that it's correct - and while "close enough is good enough" is definitely true in our own drawings, it's important that we always push ourselves to catch even those small, insignificant discrepancies in exercises like this, lest we plateau in our development. All of that is to say that I'm glad to see that you're continuing to be diligent with those checks.

There's just one small point I wanted to offer. Basically it has to do with the relationship that exists between the shift in scale from one ellipse to the other, and the shift in degree from one ellipse to the other. Both of these "shifts" represent the rate of foreshortening with which the object or form is being depicted, which in turn tells the viewer just how much of the structure's length exists to be measured visually right there on the page, versus how much is hidden in the "unseen" dimension of depth. The more the form turns to face the viewer head-on, the less of that length can actually be depicted on the page, forcing us to use some other visual cue - foreshortening - to convey that information to the viewer.

Because both shifts represent the same thing, they operate in tandem - meaning, if the shift in overall scale is really dramatic (where the side edges of the cylinder converge quickly, making the far end squeeze down in its overall size), then it should also be matched with a similarly dramatic shift in degree, meaning the far end should also be quite a bit wider, proportionally speaking, than the ellipse on the closer end. It doesn't need to be extremely precise - it's just more of a general rule that if the far end is going to be way smaller, it should also be way wider, and if the far end is going to be roughly the same scale as the closer end (maybe only a little smaller), then so too should its width not change much. If we look at 95 on this page, we've got a case where the scale shift is more dramatic, but the degree doesn't change much, and so this is the sort of thing we want to avoid. The viewer won't necessarily be able to tell what's wrong, but they will pick up on something being off.

Continuing onto your cylinders in boxes, your work here is similarly well done. This exercise is really all about helping develop students' understanding of how to construct boxes which feature two opposite faces which are proportionally square, regardless of how the form is oriented in space. We do this not by memorizing every possible configuration, but rather by continuing to develop your subconscious understanding of space through repetition, and through analysis (by way of the line extensions).

Where the box challenge's line extensions helped to develop a stronger sense of how to achieve more consistent convergences in our lines, here we add three more lines for each ellipse: the minor axis, and the two contact point lines. In checking how far off these are from converging towards the box's own vanishing points, we can see how far off we were from having the ellipse represent a circle in 3D space, and in turn how far off we were from having the plane that encloses it from representing a square.

In checking your line extensions correctly and consistently, you've continually armed yourself with ample information upon which to base your adjustments, ensuring that you're always pushing yourself forward with every subsequent page of the exercise. While there's always room for improvement in the estimation of those proportions, you've made excellent headway and should be well armed to dive into the next lesson.

I'll go ahead and mark this challenge as complete.