If you want to check the chart out with the circles, just click on the upper right corner of the chart and "make it mine". That way you can work with it yourself. When moving the circle (if you do and if you want to check the chart), make sure you only move the dotted line in the circle center. Don't touch the circles at the end of the dotted line or it will change the shape of the circle. I zoom in to make sure I don't affect the circles size or shape when moving it. These distances repeat, that's why I keep them one size and shape.
There is an easier way to check for distance. Just look for 2 points away from a center that look like they could be the same distance if the chart was scaled perfect. Use the black circle "icon" in the tool box (hole in the middle). There are a whole bunch of new icons in there. It keeps a perfect circular shape no matter what the scale, so by zooming in and out until the points are covered you can set the scale from it. There is a fine vertical line in the middle of the "circle icon",don't move the sides, just the top and bottom to change the overall size of the circle. Moving the sides makes it elliptical.