The term user equivalent range error (UERE) refers to the error of a component in the distance from receiver to a satellite. These UERE errors are given as ± errors thereby implying that they are unbiased or zero mean errors. These UERE errors are therefore used in computing standard deviations. The standard deviation of the error in receiver position, σ σ r c , is computed by multiplying PDOP (Position Dilution Of Precision) by σ σ R , the standard deviation of the user equivalent range errors. σ σ R is computed by taking the square root of the sum of the squares of the individual component standard deviations.