Error is defined as the difference between the measured as we will as the true value (as per standard) . One of the methods of measuring an unknown quantity is to measure it in terms of a standard quantity of a known accuracy. Obviously, the accuracy of the measurement will primarily be decided by the accuracy of the standard. Metrology is generally defined as the science of measurement. This, of course, includes its application to a huge range of measurements in science, industry, the environment etc. The measurement provides us with a reference for our daily life in the measurement of time, weight, length as we will as all the hundreds of measurements that influence us .