How Large Is Large Print? A Fluent-Reading Specification Labelled by the Acuity It Serves

'Large print' is sold as a point size with no stated reader in mind, and much of it is not large enough for the readers it names. This paper derives the print specification from letter geometry and the established finding that fluent reading requires print about three times the reader's acuity threshold - the critical print size. At a 40 cm reading distance, a reader with 6/18 acuity needs capitals of about 5.6 mm, roughly 22 point; the common 16-to-18-point 'large print' label serves that reader only marginally, and a reader with 6/60 acuity needs about 74 point, capitals of 18.4 mm, at which a standard page width holds only about 17 characters per line. The specification proposed labels editions by the acuity they serve fluently at 40 cm, and sizes the page, margins, and binding from the characters-per-line arithmetic rather than shrinking a standard layout's margins to fit oversized type on an undersized page. This study is simulated, not measured.