01
Decide which pressure represents the job
Prefer measured station pressure near the time and elevation of the readings. Use the elevation estimator only when an average standard atmosphere is adequate, and label the result as estimated. Weather systems can move actual pressure away from that estimate.
Confirm absolute pressure units. Gauge pressure and sea-level-reduced weather products are not interchangeable with station pressure.
02
Keep measured T and RH; change pressure context
Temperature and RH readings do not need an invented altitude correction. Recalculate the complete state using site pressure. Pressure-sensitive outputs will change because dry-air partial pressure and mixture volume change.
Generate a separate chart at site pressure rather than placing the corrected state on sea-level geometry.
03
Verified correction example
For 25 °C and 50% RH, sea-level 101.325 kPa gives 9.883 g/kg, 17.889 °C wet bulb, 0.858 m³/kg and 1.1770 kg/m³ moist-air density. At 84.6 kPa, the values are 11.874 g/kg, 17.460 °C, 1.031 m³/kg and 0.9815 kg/m³.
Dew point remains 13.864 °C in this controlled example because temperature and RH establish the same vapor pressure.
04
Apply the corrected result
Use site density when converting actual volume flow to mass flow. Use site humidity ratio and wet bulb for balances and evaporative interpretation. Retain the pressure with exported states so another reviewer can reproduce the result.
If comparing standardized flow, convert both the actual and reference states explicitly rather than substituting a standard density without explanation.
05
Limits and next action
The standard-atmosphere estimator does not forecast weather, and the perfect-gas core omits non-ideal high-pressure effects. Instrument uncertainty may exceed small modeled changes.
Next action: compare measured station pressure with the elevation estimate, calculate both states, and state why the chosen pressure is fit for the decision.