[DaiPlusPlus]

> If you assume the vertical axis and gravity are aligned

Gravity's vector is not the same as earth's surface-normal though - if you stand at the base of Mt. Everest then gravity is slightly angled compared to the curvature of the earth at that point.

[caf]

There isn't really a local good reference for "earth's surface normal" at the scale we're talking here anyway, though - it seems that what matters is the divergence between the gravity vector at one end of the factory and the other.