The Global Positioning System makes corrections for receiver clock errors and other effects but there are still residual errors which are not corrected. The standard deviations, σ R {displaystyle \ sigma _{R}} , for the coarse/acquisition (C/A) and precise codes are also shown in the table. σ R {displaystyle \ sigma _{R}} is computed by taking the square root of the sum of the squares of the individual component standard deviations. These x, y, and z components may be components in a North, East, Down coordinate system a South, East, Up coordinate system or other convenient system. e = e x x ^ + e y y ^ + e z z ^ {displaystyle mathbf {e} =e_{x}{hat {x}}+e_{y}{hat {y}}+e_{z}{hat {z}}} where bold denotes a vector and x ^ {displaystyle {hat {x}}} , y ^ {displaystyle {hat {y}}} , and z ^ {displaystyle {hat {z}}} denote unit vectors along the x, y, and z axes respectively.

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