RTK stands for “Real Time Kinematic”. GPS RTK receivers provide real time position at centimeter level accuracy, on moving vehicles.If GPS is a fifty-watt bulb and Differential-GPS a spotlight, then RTK is a laser. RTK uses the inherent properties of the microwave satellite signals to measure positions one hundred times more accurately than most Differential GPS receivers.This paper presents a breakthrough in global positioning technology, since RTK can now be done in environments where it was previously impossible. Until now RTK has relied upon dual frequency signals from the GPS system. Both frequencies were needed to get the extra measurements needed for RTK to work. We can now get the extra measurements from another GPS-like system, GLONASS. This gives us dual-system RTK. Dual-system RTK has the advantage that there are more satellites in view, so that we now have RTK operating in environments where it would not work before. Specifically, dual-system RTK operates when large parts of the sky are blocked, such as in a mine-pit, or an urban canyon. Furthermore, dual-system RTK provides order of magnitude performance improvement over GPS-only RTK, while reducing the cost of the technology.