The User Equivalent Range Error (UERE) emerges from a combination of factors including inaccuracies within the satellite navigation message, the potential disruption of satellite orbits due to perturbations, and the reliability of the satellite's clock stability. UERE is the maximum position error anticipated by the user and can be computed as the square root of the sum of all individual errors squared (ionospheric propagation delay, satellite clock error, satellite orbital variations, multipath propagation). UERE is therefore the value of all residual errors affecting the receiver position even after corrective actions have been taken.

The actual position error is however not only affected by UERE. Another factor is the Geometric Dilution of Position (GDOP). In systems that determine positions using intersecting lines, like GNSS, the arrangement of the satellites in the sky has a big impact on how accurate the calculated position can be. When the satellites are close together in the view of the GPS receiver antenna, the angles at which the position surfaces intersect become less favorable. This results in a reduction in accuracy, known as a high dilution of precision.

• The total position error can be computed by multiplying UERE by GDOP.