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I have data from an aircraft which I am trying to understand. One column contains the baro corrected altitude (in ft, e.g. 256) and another the pressure altitude(also in ft, e.g. -44). The two example data points given were measured at the same time.

I have issues finding a definition of the baro corrected altitude. How is it defined and how does it differ from e.g. pressure altitude or other types of altitudes?

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    $\begingroup$ A baro corrected altimeter is corrected for variations in local pressure and altitude. You will find the altimeter should read field elevation when the altimeter setting is correctly entered (within 75 feet). $\endgroup$
    – wbeard52
    Commented Mar 7, 2021 at 0:02

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Although, I can not find an FAA reference for baro corrected altitude, my understanding is that baro corrected altitude is the Indicated Altitude on a pressure sensitive altimeter when the Kollsman Window is set to the correct current barometric pressure. This may be different than the Indicated Altitude on a non-adjustable/settable altimeter. It may also be different than the Indicated Altitude on a pressure sensitive altimeter set for a non-current altimeter setting.

In contrast, Pressure Altitude is the height above the standard datum plain set at an altitude where the barometric pressure is 29.92 inches of Mercury. You would get Indicated Altitude to match Pressure Altitude by setting the altimeter Kollsman Window to 29.92 inches of Mercury. 5is may not represent the height above Mean Sea Level.

True Altitude is the height above the 19 year average Mean Sea Level. It is consistent regardless of barometric pressure, temperature, humidity, geographic location, etc.

Pressure Altitude is the True Altitude adjusted for non-standard barometric pressure. Indicated Altitude may differ from True Altitude based on what barometric pressure (if ant) is used to calibrate the altimeter. Having to use an altimeter setting from a weather observation (ATIS) not located at the field of use or one that has not yet updated to current.

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    $\begingroup$ @JanHudec - Per the Airplane Flying Handbook, “Pressure altitude is the height above the standard datum 29.8 112 plane (SDP). The aircraft altimeter is essentially a sensitive barometer calibrated to indicate altitude in the standard 29.92 0 atmosphere. If the altimeter is set for 29.92 "Hg SDP, the altitude indicated is the pressure altitude—the altitude in the standard atmosphere corresponding to the sensed pressure.” $\endgroup$
    – Dean F.
    Commented Sep 7, 2021 at 21:54
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    $\begingroup$ @JanHudec - “The SDP is a theoretical level at which the pressure of the 30.5 atmosphere is 29.92 "Hg and the weight of air is 14.7 psi. As atmospheric pressure changes, the SDP may be below, at, or above sea level. Pressure altitude is important as a basis for determining aircraft performance, as well as for assigning flight levels to aircraft operating at above 18,000 feet.” $\endgroup$
    – Dean F.
    Commented Sep 7, 2021 at 21:55
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    $\begingroup$ An aircraft altimeter is essentially a sensitive barometer, which is exactly the reason pressure altitude is the pressure expressed as altitude in ISA. The instrument only measures pressure, so it can only indicate pressure. The “SDP” is superfluous. You have pressure, so you have to find the point in ISA where it occurs and subtract that height from your current position to find SDP… but you already found the height, so you just call it your pressure altitude and don't need to bother even defining the SDP. $\endgroup$
    – Jan Hudec
    Commented Sep 8, 2021 at 5:39
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    $\begingroup$ More importantly, the “SDP” is not well defined for the whole air column. If two aircraft are flying at FL060, that is 6,000 ft pressure altitude, and FL120, that is 12,000 ft pressure altitude, but it's very, very cold, they may easily be only 5,000 ft apart. That means the “SDP” for the first is 1,000 ft higher than “SDP” for the other. Such definition is pointless (there is, unfortunately a bunch of pointless things in the Airplane Flying Handbook). $\endgroup$
    – Jan Hudec
    Commented Sep 8, 2021 at 5:43
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    $\begingroup$ Density altitude is a different thing. Density altitude is the density expressed as altitude in ISA where that density is expected. It can be calculated from pressure altitude and temperature, but it is not a pressure altitude corrected for temperature, it is a different thing. $\endgroup$
    – Jan Hudec
    Commented Sep 8, 2021 at 5:46

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