Ford has beaten General Motors for the first time in nearly a century, in terms of number of US factory workers. Ford has 50,703 to GM's 50,300 or so.
Answers. Well, the simplest answer is that the astrolabe pretty well had to be used at night and could not be used in bad weather. The compass, which relys on the magnetic field of the Earth rather than a visualiztion of the stars, works at any time, and in any weather.
As a navigation aid, the two basic uses of the magnetic compass is to allow the user to determine the azimuth or direction in magnetic degrees of a desired diration, and to set a direction again in magnetic degrees on the compass using a rotating bezel and follow that azimuth (dead reckoning).