Cap the Measure

Reading is a sequence of saccades ending in a return sweep to the next line. The longer the line, the further that sweep travels and the more often it lands on the wrong one, which is why a full-width paragraph feels tiring even when every word is legible. impeccable's detector estimates characters-per-line as rect.width / (fontSize * 0.5) and flags anything above 85, so a max-width of 65ch to 75ch on the prose container keeps you well clear without constraining the page around it.