If the OP has an Aladdin system in his Monaco, it does use a pressure gauge of sorts. It can be calibrated, as I say if it is an Aladdin. His manual should tell him how to do it. He can PM me for specific instructions if he'd like. Almost all the Monaco products use this system. The problem, holstien13 is that in many cases they mounted them so that "****" could interfere with the readings. My tanks read very accurately, especially the fresh water that the OP mentioned.