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The diagram below illustrates the distinction between systematic and random errors. Systematic errors tend to be consistent in magnitude and/or direction. If the magnitude and direction of the error is known, accuracy can be improved by additive or proportional corrections. Additive correction involves adding or subtracting a constant adjustment factor to each measurement; proportional correction involves multiplying the measurement(s) by a constant.
Unlike systematic errors, random errors vary in magnitude and direction. It is possible to calculate the average of a set of measured positions, however, and that average is likely to be more accurate than most of the measurements.
![Systematic error is a group of errors away from target close together & random error is errors scattered all over.](/natureofgeoinfo/sites/www.e-education.psu.edu.natureofgeoinfo/files/image/quality_sys_random.gif)
In the sections that follow, we compare the accuracy and sources of error of two important positioning technologies: land surveying and the Global Positioning System.