Unfortunately, there are some drawbacks associated with the procedure of epoch-wise clock estimation. One of the consequences is the need to observe at least four satellites at the same time to compute a position because we need to solve for three coordinates and one clock offset. Another effect is the degraded vertical position accuracy due to the fact that only satellites in the hemisphere above the horizon are observed. This asymmetry leads to significant mathematical correlations between the estimates of the receiver clock corrections, troposphere parameters and the station height