Advanced Perspective Drawing (Perfect Squares, Cubes, and How to Rotate Objects)

There have always been some perspective related problems that I couldn't find a satisfying answer to so I figured them out in my own way and made a series of three videos on the subject. Although I'm still slightly puzzled as to why they work, they do work (I've checked against 3d models).

I know there aren't many artists on here which is a shame, but I hope some of you will find this useful nonetheless if you tend to draw out your designs. If you want to see more drawing tutorials, check out my youtube channel. I only post videos if I feel they have some clear instructional goal (how to this/that).