The significance of uncertainty must be known as the performer of the test to eliminate any error which carrying out testing as it is a part of measurement. The uncertainty of measurement defines the rate of lowest possible deviation from the true value and it is also defines the level of confidence. Quality of analysis has assumed great significance in view of the fact that measurement provides the very basis of all control actions. The analysis process is at best an estimate of or approximation to the true value. The uncertainty of measurement is a right tool, associated with the result of a measurement that characterizes the dispersion of the true value which could reasonably be attributed to the measurand.