"Gravity" Contactless water level sensor, anyone?

Oh btw, I see that when they provide the small cirtcuit board that links the sensor to the specific board, the pulse switch on the board acts as "calibration", but when used without the board, the "mode" wire, seems to toggle between Normally Open o Normally Open output, is this right? I wonder how the "mode" switch has a different function with no logic in between