This is the point I noted out of pure interest Steve, it doesn't create a perfect circle. Create a circle with the ellipse tool. size it to 300x300px. Create the circle via your quick shape tool method. set it to 300 x 300px. Select both and align together centrally. Zoom into top left side in wireframe, there is a gap. Not at the top, bottom, left or right sides but at the intermeadiate points nw, ne, se & sw.
So it creates a circle that for all intended use is a near enough circle, but not the perfect circle
Bookmarks