Recent work has shown that the underlying assumptions of the Global
Positioning System (GPS) are incompatible with a number of conclusions of
conventional relativity theory, including Fitzgerald-Lorentz contraction (FLC) and
the supposed ambiguity in the relative rates of clocks in motion. The challenge is
therefore to amend relativity theory so as to bring it into full consistency with the
experience of the GPS methodology. This goal must be accomplished while at the
same time avoiding conflict with other predictions of relativity theory that have
received ample experimental confirmation over the years. It is shown that this can
be done by eliminating an undeclared assumption in Einstein’s derivation of the
Lorentz transformation (LT) and replacing it with the GPS axiom of the strict
proportionality of clock rates in different rest frames. The standard relativistic
velocity transformation still retains its validity thereby. However, the
relationships between respective measured values of observers in relative motion
for the same quantity are determined in the revised theory with the aid of a simple
scaling procedure in each case.