I'm curious as the doubling question is quite confounding for some of us. If we want to truly detect doubling should we never use anything over 20x, unless to verify the 20x finding? Is there a loose rule like this exists? With tons of magnification light can shadow and make doubling appear. To combat that I turn the coin 360 degrees observing to try to make a determination. Even then, I'm not scoring points. The pond is getting full.