Since the 1984 edition of the Vocabulary, there has been an extraordinarily quantity of activity on the subject of quality assurance, including the quality assurance of measurements. This has been stimulated by advances in science and manufacturing technology, and in the political and economic climate of supranational and global markets. With this has come the realization that traceability is not a meaningful end in itself, but is a component of a quality assurance system. Either definition of traceability implies that a reliable calibration interval for the standard can be established, although none of the definitions above mention time. Readers of these pages will be aware that I have long argued that fixed calibration intervals do not make sense for standard resistance thermometers.
Standard thermometers are delicate things.
It has been said, correctly, that to put one down on a laboratory bench with enough force so that one can hear it touch nay strain it out of calibration. Thermometers shipped for calibration may be strained during return shipment. Other hazards, of handling and of use, can be enumerated. However, if one is prepared to check a thermometer at the triple point of water after every transportation, and after every use, and convey these measurements to a permanent record or control chart, assurance of calibration can be maintained as it can be for no other reference standard. Thermometrists are fortunate in having so reliable a way to control quality of measurement, and to assure that their instruments are traceable to the very definition of the Temperature Scale.