Circles do not exist.

Since roughly the mid 80s all "high quality" print jobs have been done either in PostScript or, nowadays almost exclusively, in PDF. They use the same basic drawing model, which does not have a primitive for circles (or circle arcs). The only primitives they have are straight line segments, rectangles and Bézier curves. None of these can be used to express a circle accurately. You can only do an approximation of a circle but it is always slightly eccentric.