This recommendation specifies the metrological and technical requirements applicable to methods of calibration and test for atmospheric pressure, measures and to their initial and subsequent verification. It has relevance to the following types: a) Mercury barometers having a permanent reference vacuum. b) Barometers, for example aneroid barometers, with an elastic sensing element, a permanent reference vacuum and an indication, which may be either analogue, with a pointer and a dial, or digital.