Starting with your cylinders around arbitrary minor axes, for the most part these are well done - you're improving on the overall control of your ellipses, while maintaining a good deal of confidence in their execution. I'm also seeing some variation in rates of foreshortening, although I definitely would have liked to have seen more. Most of these were very shallow, to the point where I wasn't always sure whether you were keeping convergence towards a far off point in mind, or if you'd just decided to try and keep those side edges parallel on the page itself.

Just remember - because vanishing points going to infinity is something that only occurs when the object in question is aligned perpendicular to the angle at which the viewer is looking at the object, it's an uncommon thing unless it is an intentional part of how the form is being oriented. When rotating things freely as we're doing in this challenge, it's basically not going to happen. That means there should be at least some convergence for all of our parallel edges, even if only very slight. Otherwise we end up in a situation where we're telling the viewer that there is absolutely no foreshortening, and therefore the cylinder has no actual distance between its opposite ends. This of course can't be true, resulting in a visual contradiction.

To that point, I did notice a couple places where you ended up with other similar visual contradictions, although not many. Foreshortening is represented in two ways - the shift in scale from one end to the other (far end is smaller than the closer end), and the shift in degree where the far end is wider than the closer end. These "shifts" have to be consistent - we can't have a lot of one, and very little of the other.

If you take a look at 78, this one looks pretty strange, because it's got a visible shift in scale, with the far end being smaller, but the degree remains roughly consistent. This makes the viewer wonder whether this form is longer (which is what more dramatic foreshortening implies), or whether it is shorter (shallower foreshortening).

Long story short - keep these aspects of foreshortening in mind.

Moving onto your cylinders in boxes, it is worth noting that a lot of the boxes suffer from similar issues, where the convergences seem to be parallel on the page by design. For example, on number 277, you've got a bit of convergence for the edges going off to the left, but on the right side they seem to be very parallel. It's totally okay for these things to happen as you practice, as long as they're not intentional. Again - you should be aiming to have these lines converge at least a little bit (as they do on the left).

Aside from that, you're doing a good job of checking all the line extensions - doing so with the lines associated with each ellipse has helped you develop a good sense on how to construct boxes with two faces which are proportionally square. That's the main purpose of this exercise, since the focus on the ellipses' minor axes and contact lines cause us to focus on making adjustments and tweaks that'll have them converge towards the box's own vanishing points. Of course when this occurs, it means the ellipses are representing circles in 3D space, and therefore the planes enclosing them would be square.

The development of these instincts should serve you well throughout the next couple of lessons, so good job on that front.

All in all - watch your foreshortening. I'll go ahead and mark this challenge as complete.