Horizontal vs. Vertical Tank Orientation

Why do I need to designate the orientation of my tank?

Because of the different geometries of the tanks, there are different calculations used in our server for different types of tanks. Assigning your tank orientation gives you accurate tank level data. 

How do I know if my underground tank is horizontal or vertical?

If your tank is underground it is most likely horizontal. You can double check by looking at your gauge face - there should be some small writing indicating the type of tank the face is meant for.