GUIDE TO PURCHASE,
INSPECT AND MAINTAIN DIGITAL MEASURING INSTRUMENTS

GB/T14899—94 is a Chinese National Standard for Digital Caliper.

ISO/DIS13385—96 is an International Standard for designing of Digital Caliper and technical requirements of Metrology. The former standard is applied in most of the state-run enterprises in China; while the latter one is applied in overseas markets and in most of the foreign-funded enterprises in China. ISO/DIS13385-96 is a stricter international standard. It requires cautious verification for errors of a value measured when an inside measurement (like measuring the diameter of a hole) is done. The reason is very simple for that. When measurement of the diameter of a hole (especially a small hole) is done by a new digital caliper, an uncertainty in value should be assured. GB/T14899—94 Chinese National Standard is followed by old national standard largely. It only verifies the deviation of inside measuring jaws and parallel level of measuring faces without verifying the measured value of “inside measuring”. So much consideration has been given to leave leeway in advance for its loss of abrasion that the exactness of “inside measuring” is ignored and that serious measuring error is often made when the diameter of a hole (especially the diameter of a small hole) is measured by a new digital caliper. It makes it more difficult for manufacturers who adopt Chinese National Standard before 1996 to carry out ISO/DIS13385—96 (International Standard). In order to be in accordance with the standard of international markets, Guanglu has been carrying out the above-mentioned international standard most of the time except when it’s not required by some special domestic clients.