Congratulations on getting and installing your wx station Dan! Lots of fun ahead now.
To give you more confidence in your rain sensor use a manual rain gauge setup next to the station sensor and compare. Be absolutely certain that the station sensor is level in all directions. After several comparisons you can start "calibrating" (if you need to) the station sensor to the manual gauge. This can be done several ways, software and hardware.
Welcome to the addiction!
Dan