'Traceability' means that the measurement results can be related to a stated reference by an unbroken chain of accredited comparisons. The stated reference usually refers to national or international standards - in the UK these would be standards maintained at the National Physical Laboratory. Traceability gives the user confidence that his/her measurements agree with the National Standards within the stated uncertainty. It also ensures that the measurements will be equivalent to those made using different instruments from different suppliers. Since it has been demonstrated that the standards maintained at the NPL are in agreement with those held at other National Standards Laboratories, the user can be sure that measurements made in the UK are equivalent to those in other countries. This is particularly important when importing or exporting goods. Traceability can be achieved by calibrating the device at the National Standards Laboratory, or, in the UK, at a laboratory accredited by UKAS whose standards are themselves calibrated with traceability to NPL's.