Editing Gravity anomaly (section)

===The free-air correction===
{{main|Free-air anomaly}}
The next correction is the free-air correction. This takes into account the fact that the measurement is usually at a different elevation than the reference ellipsoid at the measurement latitude and longitude. For a measurement point above the reference ellipsoid, this means that the gravitational attraction of the bulk mass of the earth is slightly reduced. The free-air correction is simply 0.3086 mgal m<sup>−1</sup> times the elevation above the reference ellipsoid.{{sfn|Lowrie|2007|pp=79–80}}

The remaining gravity anomaly at this point in the reduction is called the ''free-air anomaly''. That is, the free-air anomaly is:{{sfn|Lowrie|2007|pp=83–84}}
<math display="block">\Delta g_F = g_m + (\Delta g_{FA} + \Delta g_T + \Delta g_\text{tide}) - g_n</math>