This chapter takes the standard uncertainty calculated in the previous chapter and shows how to apply a statistical confidence in order to determine the expanded uncertainty, which is commonly referred to as “the uncertainty of a measurement.” The chapter demonstrates how uncertainties quoted at one level of confidence (e.g., on a calibration certificate) can quickly be converted to a different level of confidence. The concept of uncertainty budgets is introduced, and used to show how they can be used to identify where effort (money!) needs to be put to improve the accuracy of a measurement, and where extra effort is unwarranted.