Detail from a pen plot of large concentric arcs in magenta, gray, and black ink. One arc with origin in the bottom left is large enough to reach to the center of page, obscuring a large arc below it. Some lines are thicker than others. This detail shows the area of the center of an arc in the upper left. The pen strokes are clearly visible.
https://files.mastodon.social/media_attachments/files/113/011/783/980/627/533/original/065d4c903d2003d1.jpeg