Via sister site MachineControlOnline... Global Navigation Satellite Systems, or GNSS have systematic errors in the range of 10 meters.
That is to say if a user turns on a GNSS device and there is no additional input other than the signals from the navigation satellites, the receiver’s position on the planet can be calculated with some amount of confidence to a precision of 10 meters.
The concept of Differential GNSS was introduced over a decade ago and relies on a basic principle as follows: The amount of error in one receiver will be the same amount of error as another receiver that is nearby at the same moment in time. By putting one receiver on a tripod over a known point and collecting positions, another receiver can move about a job site making measurements that can be differentially corrected. Since the tripod is not moving and we know the precise location over which it is placed, we can take the calculated position and subtract the differences from the known position each second in time. By matching the rover data to the base station data, the rover’s position can then be differentially corrected.
Originally, this process was accomplished after all the data had been collected by using office software to calculate the differences (post-processing). The newer process utilizes a real-time connection between the base and the rover. In the most precise modes, the rover position can be calculated to less than an inch (1 centimeter) at 20 times per second. This technique is called RTK for Real-Time Kinematic.
Originally, this process was accomplished after all the data had been collected by using office software to calculate the differences (post-processing). The newer process utilizes a real-time connection between the base and the rover. In the most precise modes, the rover position can be calculated to less than an inch (1 centimeter) at 20 times per second. This technique is called RTK for Real-Time Kinematic. 
