`  The basic concept section is now completely pathetic.  With statements such as, ``It is sometimes incorrectly said that the user location is at the intersection of three spheres``, it is pathetic.  How could anybody who understands the navigation equations make such a statement as that.  The solution of the navigation equations locates the user at the intersection of n spheres so it is certainly at the intersection of 3 spheres.  Apparently some people just want to show their ignorance by making statements such as this.    `