You are probably in the field and someone has poured a circular slab. However, the didn’t leave you the origin of the circle. You could also be wanting to create an arch and you need to find a spot on the shop floor to use your trammel points (large compass) to create the proper radii on your rough stock.
Fear not fellow tradespeople, follow the instructions below.
Also helpful for drafters, architects, and whoever else is trying to find that elusive center of a circle.
While we are at it, and because we LOVE geometric design based on arcs and radii. Have you ever seen a hypocycloid? Leave a comment if you can figure out what is going on with it. Think dynamic movement.