The increasing need for known accuracy and uncertainty and the need to have consistent and comparable standards internationally has led to the establishment of national laboratories. This definition states that the calibration process is purely a comparison, but introduces the concept of measurement uncertainty in relating the accuracies of the device under test and the standard. The formal definition of calibration by the International Bureau of Weights and Measures (BIPM) is the following: "Operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties (of the calibrated instrument or secondary standard) and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication." 5.3 The early calibration of pressure instruments.5.2 Calibration of weights and distances ( c.4.5 Process description and documentation.The calibration standard is normally traceable to a national or international standard held by a metrology body. Strictly speaking, the term "calibration" means just the act of comparison and does not include any subsequent adjustment. an adjustment made to correct the error to an acceptable level.a significant error being noted but no adjustment made.no significant error being noted on the device under test.The outcome of the comparison can result in one of the following: Such a standard could be another measurement device of known accuracy, a device generating the quantity to be measured such as a voltage, a sound tone, or a physical artifact, such as a meter ruler. In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. For the statistical concept, see Calibration (statistics). This article is about assessing the accuracy of a measurement device, like a scale or a ruler.