The multiplicative factor that modifies ranging error; Its sole cause is by the geometry between the user and his set of satellites. AKA DOP or GDOP

an intentional error controlled by the DOD to reduce the accuracy of GPS receivers. This inaccuracy requires the use of differential correction to achieve the level of precision required for the site-specific management.

Since a GPS receiver determines position by triangulation, when the GPS satellites that are being received are clustered too close together, the positional accuracy determined by the receiver is diluted. The wider the angle between satellites, the better the measurement.