How to Draw Circles in Perspective like a Geometer

There are a lot of tutorials and guides in the net on the subject of drawing ellipses, but they — invariably to my knowledge — follow the same formula: project a square in perspective, then sketch an ellipse inside it with guides.

The ghost of Euclid cries in agony every time someone draws an ellipse like that. This guide will tell you how to do it precisely using the classic tools: a ruler, a compass, and additionally a piece of string and two pins, to render the ellipse itself.

Heliocentric Helical Hoop World

How about putting a hoopworld around a sun? And another, while we're at it. Having read about megastructures I haven't yet come by anything like this, which probably means a) I haven't looked deep enough, or b) it's so ridiculous that nobody has bothered putting it down, or c) neither. Assuming c) and waiting anyone to submit evidence for a) or b), here are some properties and problems of this kind of a world based on a limited grasp on physics.

Wax Tablets

From antiquity up to the 19th century wax tablets were the way to take notes quick. Infinitely reusable and easier to use than ink on papyrus or parchment. Here are two versions I made.