Triangles provide a simple and inexpensive alternative to the parallel rule for transferring a bearing or course from the compass rose to the ship’s position on a chart. These triangles are made of wood.
This is an example of the sailing directions included in The English Pilot, Fourth Book. They describe sailing along the Maine coast, though the top of the page says Newfoundland. See online at Boston Public Library electronic access.
This box of instruments was owned and used by Captain Andrew M. Ross of Searsport aboard the ship Henrietta. The dividers were used for many position plotting and calculating purposes, including measuring distances traveled, plotting offsets in celestial sight reductions, and assisting in calculations with the gunter scale.