I find it hard to create a collection of shapes that are different sizes, yet have the same thickness of line. Currently I create shapes with the tools on the left, such as a circle. when I am done creating a circle I find that if I want to make it a little smaller (reduce diameter), the thickness of the line is also reduced when the circle is modified by the provided handles. Is there a UI feature I am missing that will allow me to change the size and shape of a object, without changing it's line size?

thanks for fun app. I apprieciate any help!