“I knows him!” and, after a few convulsive efforts, the red legs took the shape of a pair of compasses, and the intelligent pupil triumphantly shouted, “It’s a We, Dranpa, it’s a We!”

One of the simplest techniques used by Tycho in 1563 was to hold a pair of compasses close to his eye, with the point of one leg of the pair on a star and the other point on a planet of interest—say, Jupiter.

The most common type of apotropaic mark is the daisy wheel, or hexafoil, which is often a six-petal “flower” drawn with a pair of compasses.

The public body Historic Britain says they are often carved into the shape of a daisy wheel, which looks like a six petal “flower” drawn with a pair of compasses in a single endless line that was supposed to confuse and entrap wicked spirits.

“He would draw out of a little drawer under his table, and show them a pair of compasses with one of the legs broken; and then, for his ruler, he used a sheet of paper folded double.”