frame longitude latitude altitude time in the same way the receiver may calculate its velocity along the n satellite axes and deduce therefrom its velocity in a four dimensional terrestrial frame however given that only four satellites are necessary for determining a position or a velocity whereas the measurement is taken on n satellites with n gt 4 there is redundant information if the measurements are subject to errors measurement noise on each axis the coincidence between the various measurements will not be perfect this means that if one group of 4 satellites is chosen form the n the coordinate change will lead to one position and one velocity vector in the terrestrial frame but if another group of 4 satellites is chosen this will lead to a slightly different position and a slightly different velocity vector the receiver therefore calculates for example using a least squares method the most probable position and velocity resulting from use of the n satellites this method will be returned to in more detail furthermore the receiver may also calculate an estimate of the error resulting from use of the n satellites that is to say an estimate of the divergence between the n measurements it may determine whether this divergence exceeds an acceptable threshold and conclude therefrom that the measurement should be rejected because of this excess lastly it may calculate an estimate of the measurement error coming from a particular satellite perform classification of the errors generated by the various.