The <i>Tondo e quadro</i> ("Circle and Square"), a visual measurement method of calculating trigonometric values for navigation, from the first page of the ten-sheet atlas by Venetian cartographer Andrea Bianco, dated 1436.  Held by the Biblioteca nazionale Marciana, Venice.
Andrea Bianco
1436
Atlante Bianco, Biblioteca nazionale Marciana, Venice (<a rel="nofollow" class="external text" href="http://geoweb.venezia.sbn.it/geoweb/iscgi/archiweb.dll?service=direct&amp;lang=0&amp;uid=000004&amp;session=000000&amp;fld=B&amp;value=029110">no.</a>)