Zenith

I put the overhead point off center, where the frame crops its rings, and let the ground carry the measurement: bands of equal altitude narrow outward, the ruling thickens and closes, and the horizon is a rim of solid black, not a line. In one wedge I exchange the inks, so the same measurement reads black at the point and paper at the rim. Only a dot on bare paper marks the point; the graded field is the evidence.