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https://twitter.com/BetsyShirley/status/1534899004680589312An "Em Quad" is a perfect square of the body size in metal type. So, a 14pt Em would be 14pts high and wide. (Though, in 1480 "point sizes" weren't yet a thing.) Ems, or quads, were clearly used in the earliest days of printing as semi-standard post-period spacing.