Compasses (plural) usually refers to the instrument we would call dividers today. They may have two points, or a point and pen or pencil. As the picture in Mission's post shows, the points may be interchangeable. Although that beautiful set would be used for drafting rather than navigating. For navigation they typically have two points and are used for measuring or marking off distance on a chart rather than drawing arcs. They were probably of the two pointed type with loops at the top near the joint.