| Calculation | Description |
|---|---|
| QFE (pressure at field elevation) | Barometric pressure value reduced to TDZ elevation. |
| QNH | Barometric pressure at a place, reduced to mean sea level (MSL). The "reduction" is made by assuming standard atmosphere. |
| QFF | Barometric pressure at a place, reduced to mean sea level (MSL). The "reduction" is made by using the actual temperature at the time of observation. |