Quelques explications sur le tracé des cadrans solaires 1640
A 1640 French manuscript-style treatise on laying out sundials, attributed to Christoph Clavius and held by the Smithsonian Libraries, written for dialing students and instrument makers. The single picture is a handwritten diagram of a meridian line, a gnomon and a horizontal sundial plane with hour lines drawn in pen on aged paper, useful to a designer wanting hand-drawn geometric construction marks.
