A standard is something established by authority as a rule for the measure of quantity, weight, extent or quality. Accuracy of measurements should be stated as a probability relative to an accuracy standard. For example, this length measurement has a 95% probability of falling within one centimeter of exactly one meter as given by the ISO standard meter length. Some people might state this as 1.0m 1.0cm but this discounts the probability value which can make a big difference in the perception of accuracy as discussed above.