Initial Mesh Levels

In Flow Sim, there is the initial mesh settings box:

What exactly is the difference between levels 1 through 8? Is there a reference somewhere that describes the properties of each level (e.g. I've read around the forums that auto-refinement is done at levels 6 and higher)? The documentation I have (from the Student Edition) only supplies validation examples and describes the algorithm by which meshes are generated, but does not describe each mesh level individually.

Thank you.

SolidworksFlow Simulation