GPS and relativity

According to an article in the November 2004 edition of
Scientific American, the GPS satellites' clocks have a
7 microsec per day effect due to relativistic motion
and a 45 microsec per day effect due to the lower
gravity in orbit. The two effects partially cancel, so
the net adjustment is 38 microseconds.

It is left as an exercise for the student to determine
the effect of an uncompensated time value on position
values.