Designation:D3631−99(Reapproved2011)StandardTestMethodsforMeasuringSurfaceAtmosphericPressure1ThisstandardisissuedunderthefixeddesignationD3631;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1Thesemethodscoverthemeasurementofatmosphericpressurewithtwotypesofbarometers:theFortin-typemercu-rialbarometerandtheaneroidbarometer.1.2Intheabsenceofabnormalperturbations,atmosphericpressuremeasuredbythesemethodsatapointisvalideverywherewithinahorizontaldistanceof100mandaverticaldistanceof0.5mofthepoint.1.3Atmosphericpressuredecreaseswithincreasingheightandvarieswithhorizontaldistanceby1Pa/100morlessexceptintheeventofcatastrophicphenomena(forexample,tornadoes).Therefore,extensionofaknownbarometricpres-suretoanothersitebeyondthespatiallimitsstatedin1.2canbeaccomplishedbycorrectionforheightdifferenceifthefollowingcriteriaaremet:1.3.1Thenewsiteiswithin2000mlaterallyand500mvertically.1.3.2Thechangeofpressureduringtheprevious10minhasbeenlessthan20Pa.Thepressure,P2atSite2isafunctionoftheknownpressureP1atSite1,thealgebraicdifferenceinheightabovesealevel,h1−h2,andtheaverageabsolutetemperatureinthespacebetween.ThefunctionalrelationshipbetweenP1andP2isshownin10.2.ThedifferencebetweenP1andP2foreach1mofdifferencebetweenh1andh2isgiveninTable1and10.4forselectedvaluesofP1andaveragetemperature.1.4Atmosphericpressurevarieswithtime.Thesemethodsprovideinstantaneousvaluesonly.1.5ThevaluesstatedinSIunitsaretoberegardedasthestandard.1.6Thisstandarddoesnotpurporttoaddressallofthesafetyconcerns,ifany,associatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappro-priatesafetyandhealthpracticesanddeterminetheapplica-bilityofregulatorylimitationspriortouse.SpecificsafetyprecautionarystatementsaregiveninSection7.2.ReferencedDocuments2.1ASTMStandards:2D1356Terminolog...
