This demo displays the circle given by X(t) = (a,b) + (Rcos(t), Rsin(t)). To change (a,b), type the desired expression for (a,b) in the appropriate text box in the control window and press Enter. To move the point X(t0) along the circle, or to change R, the radius of the circle, use the arrow buttons ([<], [>], [<<], [>>]), which have the same function as in the first two demos. As in earlier demos, there are "Show entire curve", "Show position vector X(t0)" and "Show Color Spectrum" options.