Hi DickO,
You don't need to use the zero calibration unless there's a problem where the AUTO button results in the coach not being level. Keep in mind that if the campground is not reasonably level, you can have challenges getting the coach level with wheels on the ground. The calibration procedure stores the current info from the leveling sensors and on future operation of the AUTO button, uses that data to determine when the coach is level.
If you need to calibrate, you first level the coach using the manual mode, using a level to determine when the coach is actually level. It's helpful to use a level that's at least several feet long to get a more accurate reading. I would suggest setting it on the floor aligned front to rear midships and then align cross-wise to check side-to-side. It's also a good idea to find a level surface so you don't have any unusual leveling challenges.