the same purpose obsolete. Bearing instruments Pelorus used to determine bearings relative to the ship's heading of landmarks, other ships, etc. Compasses Bearing compass used to determine magnetic bearings of landmarks, other ships or celestial bodies. Magnetic compass used to determine the magnetic heading of the ship. Timekeeping Marine chronometer used to determine time at the prime meridian with great precision which is necessary when reducing sights in celestial navigation. Nocturnal used to determine apparent local time by viewing the Polaris and its surrounding stars. Ring dial or astronomical ring used to measure the height of a celestial body above the horizon. It could be used to find the altitude of the sun or determine local time. It let sunlight shine through a small orifice on the rim of the instrument. The point of light striking the far side of the instrument gave the altitude or tell time. All those mentioned were the traditional instruments used until well into the second half of the 20th century. After World War II electronic aids to navigation developed very rapidly and, to a great extent, replaced more traditional tools. Electronic speed and depth finders have totally replaced their older counterparts. Radar has become widespread even in small boats. Some Electronic aids to navigation like LORAN have already become obsolete themselves and have been replaced by GPS. Electronic Travel Aid As technologies are developed, designers and engineers have also turned their attention to minority groups like people that are visually impaired. In this case , Electronic Travel Aid are developed to target the needs of visual impaired individuals for obstacle identification as well as navigation of the surrounding to enhance mobility. Not only GPS systems, there are other approaches like infrared sensors, ultrasonic sensors as well as optical technologies like cameras that are developed/ developing to enhance the navigation of the minority group. See also Douglas protractor Cras plotter Breton plotter (aka Portland plotter or Weems protractor) Navigation protractor triangle References External links How to use the dividers How to use the parallel rulers Navigational Instruments at The Mariners' Museum Navigation Navigational equipment