ASTM D 3631:2025

1.1 These test methods cover the measurement of atmospheric pressure with two types of barometers: the Fortin-type mercurial barometer and the aneroid barometer. 1.2 In the absence of abnormal perturbations, atmospheric pressure measured by these test methods at a point is valid everywhere within a horizontal distance of 100 m and a vertical distance of 0.5 m of the point. No corrections are required for readings from two aneroid barometers compared within these distances that are both exposed to ambient air conditions. 1.3 Atmospheric pressure decreases with increasing height and varies with horizontal distance by 1 Pa/100 m or less except in the event of catastrophic phenomena (for example, tornadoes). Therefore, extension of a known barometric pressure to another site beyond the spatial limits stated in 1.2 can be accomplished by correction for height difference if the following criteria are met: 1.3.1 The new site is within 2000 m laterally and 500 m vertically. 1.3.2 The change of pressure during the previous 10 min has been less than 20 Pa. The pressure, P 2 at Site 2 is a function of the known pressure P 1 at Site 1, the algebraic difference in height above sea level, h 1 − h 2 , and the average absolute temperature (degrees Kelvin) in the space between. The functional relationship between P 1 and P 2 is shown in 10.2 . The difference between P 1 and P 2 for each 1 m of difference between h 1 and h 2 is given in Table 1 and 10.4 for selected values of P 1 and average temperature. 1.4 Atmospheric pressure varies with time. These test methods address nearly simultaneous values. 1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.6 Warning- Mercury has been designated by many regulatory agencies as a hazardous substance that can cause serious medical issues. Mercury, or its vapor, has been demonstrated to be hazardous to health and corrosive to materials. Use caution when handling mercury and mercury-containing products. See the applicable product Safety Data Sheet (SDS) for additional information. The potential exists that selling mercury or mercury-containing products, or both, is prohibited by local or national law. Users must determine legality of sales in their location. 1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific safety precautionary statements are given in Section 7 . 1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

07.060