An indispensable navigational instrument; essential for orientation and dead reckoning. Originally used for navigating the Mediterranean Sea, they were later put to use on transatlantic voyages. In their most basic iteration, they consisted of a needle floating in a bowl of water. Later designs included a circle with graduated markings (compass rose), a wooden housing, and a system to ensure that it remained horizontal. This system was designed by Gerolamo Cardano, after whom it was named.