if not ? it is a beam compass, that can be adjusted to any size you need?
you would need at least 2 blocks of wood like 2" x 2" x 3" and a strip of 1/4" thick plywood, once you know how big the circle has to be?
you would also need at least 2 pieces of 24" square sheet of 3/4" thick plywood, you can create the 20" inch outside circle from one square to trace a circle to the second 24" square though you would cut out the inner circle and sand smooth the circlee with a drum sander.
for the trammel you can affix a glass cutter to one end of one block then make sure your cutter is at zero, and you can affix the second block so that a center pin would be at the 10" mark to become a center for the 20" circle.