Understanding the SEN0676 80GHz High- Precision Liquid Level Detection Millimeter Wave Sensor

I'm trying to get a better understanding of the SEN0676 80GHz High-Precision Liquid Level Detection Millimeter Wave Sensor.

First the diagram in the Wiki labels the “Empty Height” as the top of the water level which makes no sense.

Also, in the code the is a function for set/get Installation height. That makes sense and I'm presume that the variable does not change.

There then is a Range function, which does what? 

Next is the EmptyHeight function which again says its from the sensor to the water line. To me that's not what empty means.

Lastly, there is the get water level function, which I presume is the depth of the water.

Is there someone who can help clarify for me?

TIA