Excellent! Thanks

I am trying to draw an organic donut of sorts. So I have drawn freehand circles for variable cross sections and connected them with curviloft. This works perfectly except that now I am told that the diameter of the cross section cannot be any larger that 12" or smaller than 4". So I need 2 guides to work between. If I draw circles, I snap to them which ruins the freehand. But with tape measure I can only draw rectangular guides. I guess I could draw a star with line segments but it would be easier to just draw a circle. Is there any way to draw circles with the tape measure?