THESE ARE PRICED AT £45 EACH.
Two small ebony and brass style Captain Fields parallel rule. Measures 15cm x 3.5cm.
One is well worn and one has red dye on it as can be seen in the images.
Navigators use parallel rules for laying off a specific course on a chart. They were first invented in 1584 by a Frenchman named Mordente, but only became common in navigation in the 18th century.