Difference between 6 point and gradient normal map

Hi there,
I’m a Unity coder and would like to use the Embergen’s normal maps in my shaders.
The definitions of the maps in the documentation are pretty vague.
- Six Point Normal Map: Interpretation of the normals based on six angles used as an input for a flipbook shader in other 3d-packages.
- Gradient Based Normal Map: Interpretation of the normals based on a gradient used as an input for a flipbook shader in other 3d-packages.

Can somebody give me a clearer description ?