About input value at elevation in C2rcc

I am new to snap . i am doing disseration work on water quality by using snap.i am facing a problem elevation input. i am not understanding what value i want to give their exactly.Because at every value results are coming differently. please help me.what exactly elevation means what values i want to input their.please help me.

The only parameter related to elevation in C2RCC is the air pressure at sea level, that you will modify only if: you know the average air pressure is different to the one given by default the day the image was taken (you have auxiliary data); or you are working on a lake that is not a sea level and you can estimate the air pressure at that said altitude.