English: This image shows a hypothetical gravity measurement. The red point marked ${\displaystyle g_{m}+g_{tid}+g_{T}+g_{FA}}$ is the measured gravity at a point on the surface of the earth, corrected for tidal forces, local terrain, and elevation. The green point is the normal gravity ${\displaystyle g_{n}}$ calculated for that latitude and longitude, which lies on the reference ellipsoid. The difference between the two is the free-air anomaly.