<Li> 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 . </Li> <P> 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 Some Electronic aids to navigation like LORAN have already become obsolete themselves and have been replaced by GPS . </P>

Some of the instruments that were used to navigate on the seas were