GPS Error
<< Also, the satellite ephemeris being used by one reciever may be a newer or
older one than that used by the other (the ephemeris is the data sent by the
satellites that allows the reciever to calculate the satellites' position, and
it is updated periodically)>>
This is not very likely to be the case since the ephemeris data for the whole
configuration is downloaded from the satellites themselves. Receivers should
therefore be using the same ephemeris at the same time.
Rob