"One-handed Or Marine Compass, 18th Century"
"This drypoint compass, decorated with geometric patterns, can be opened with one hand, up to 180 degrees. It is made up of two arms, the upper part of which, split on one side, is semicircular in shape. At the top, a screw serves as a pivot." (Frémontier-Murphy, 2002) Used for nautical charts: it has a smaller opening capacity than the straight compass, but its shape makes it easier to grip with one hand, the other remaining available for handling the navigation ruler or pencil. This example, of a good size with entirely uncut arms, measures 16 cm in length. It can be dated to the 18th century. It is in perfect original condition, without restoration or accident. 
Le Magazine de PROANTIC
TRÉSORS Magazine
Rivista Artiquariato