Your GNSS Training Headquarters for GIS and Mapping Applications

The Department of Defense turned off Selectively Availability on May 2, 2000 which reduced GPS uncorrected positional error from approximately 100 meters to 10 meters.

Explanation of Graph Labels:

SPS- Standard Positioning Service- the normal civilian positioning accuracy obtained by using the single frequency C/A code (Coarse/Acquisition).

CEP- Circular Error Probable (horizontal only, 2D)- a statistical statement that describes a 50% confidence level.  In other words, 50% of the positions obtained will be within the stated distance from ground truth.

SEP- Spherical Error Probable (horizontal and vertical, 3D)- a statistical statement that describes a 50% confidence level.  In other words, 50% of the positions obtained will be within the stated distance from ground truth.

UTC- Universal Time Coordinated- local solar mean time at the Greenwich Meridian.  A uniform atomic time system maintained by the U.S. Naval Observatory.