ABSTRACT
It is important to remember that hardly any measurement is 'exact'. All measurements you perform have errors and faults. This chapter commences with a discussion on calibration and traceability as these are the basis for uncertainty. A calibration without traceability is of no value. Repeatability is a quite good indicator of instrument quality. With a close connection to calibration activities and accreditation, an intercomparison is a commonly used procedure to ensure that a calibration laboratory delivers good quality results. Related to the conformity assessment, there are three ways to handle the uncertainty when making a decision based on a measurement. The 'seller' can take the risk, the 'buyer' can take the risk or they both can share the risk. If the sensor or instrument a person is calibrating is a part of a system or measuring loop, the complete system or loop of course must be calibrated.
