- Inches of mercury (Hg) >> for altimetry
- Hectopascals (hPa) and millibars (mb) >> for weather map analysis
- measured using a barometer (digital or aneroid type)
METARs give both an altimeter setting and a sea level pressure. What's the difference?
- Station Pressure
- measured at the airport; the weight of the air above the station
- Altimeter Setting
- station level pressure reduced to MSL assuming ISA conditions
- MSL Pressure
- station pressure reduced to MSL using the average surface temperature for the last 12 hours
- useful in weather map analysis when patterns across different observation stations must be compared
And just for fun, here's 'Under Pressure' by Queen:
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