I am using the watering.ino example

https://github.com/m5stack/M5Stack/blob/master/examples/Unit/WATERING/WATERING.ino

How should I interpret the humidity sensor values? Is there a way to do a calibration? I get values ​​of about 2100 for the sensor in air, 1800 if wrapped in a wet rag and 1500 if immersed in water.

thanks