Alan, an easy way to centre the design for your next targe is to trace around the circle of wood onto a piece of paper, cut it out, and fold it in quarters. Now you have the centre point, and four axes. Lay the paper on your targe and prick through the centre fold with an awl or a nail. You can plan the design on the paper, and transfer the entire thing over with the awl. You can plot concentric circles by placing a nail through the centre hole and draw around it with a pencil on a length of string.

Andrew.