A fix is a position defined in relationship to at least two specific navigational aids. The tolerance of each navigational aid used at the fix position must be added together to determine the overall fix tolerance. This overall fix tolerance will change depending on the positions of the navigational aids and the fix itself.
Using conventional navigational aids, the more beacons defining a fix position the greater the fix tolerance. However the opposite is true for satellite navigation. Basically the greater the number of satellites in view the greater the position accuracy.