Discrepancies between surveys are usually attributable to two reasons. The first reason is that measurement, depending upon the tools used and the manner performed, is subject to some variation. Two surveyors measuring the same line may obtain slightly different values. Both of the values should be similar, but they will only approach the true theoretical value through repetition and statistical analysis. The second and usually more profound reason is that measurements are made from, and decisions are based upon written and physical evidence. If a survey is based upon something other than the best evidence available, discrepancies can and frequently do occur. It is the surveyor’s responsibility to seek the best evidence available, and by its very nature, that evidence is subject to interpretation. Seeking the best evidence generally takes time and effort, both of which are true attributes of a thorough survey.