Here’s an idea for checking ellipses. When I draw out the image for ellipses I draw the cross for the major and minor axis and then draw out the ellipse connecting those points. But I don’t always get the ellipse perfect and if the ellipse is off it’s noticeable so I usually do a lot of adjusting. I just hold up the jar lid at the correct distance between me and the drawing to size it up.
I line the jar lid up with the major axis and then I tilt it to see if the ellipse I drew deviates. It’s especially useful for ellipses at an angle. It’s not perfect but it gives me an idea of what to adjust.