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.