Circles should be unshaded or shaded evenly with thick and thin lines, changing at about 45 degrees.
Anthony, Gardner C. Elements of Mechanical Drawing (Boston, MA: D. C. Heath & Co., 1904)
2400×2266, 287.9 KiB
1024×966, 44.0 KiB
640×604, 24.7 KiB
320×302, 11.2 KiB