This standard requires air saturation at 0C of the sample which total vapor pressure (Ptot) is measured. Ptot is a linear combination of the actual vapor pressure of the sample and the partial pressure of the thus dissolved air. The amount of dissolved air is a function of the barometric pressure and consequently lower at high altitudes. Since this standard does not address the effect of altitude (barometric pressure), the ARV of verification samples are often not met. This problem was addressed by Mr. Ken Huang from Chevron during the section meeting, December 13th, 2018 and resulted in the creation of WK66752. Since this work item no longer exists, we have crated a follow up WK, because recently this problem was again discussed among different users. So far proposed is recommending the D6378 (triple expansion) for verification and noting down barometric pressure for D5191 readings. This works for all modern instruments. For older equipment a simple correction formula was proposed by Mr. Bob Falkiner. Mr. Alex Lau suggested to verify this in a study with about 6 labs (high altitude locations) and real check samples / gasoline instead of pure compounds.