2005 Optimax 250 XS Serial number OT998654. My boat has the square shaped Mercury Systemonitor gauge. It shows some useful information, such as fuel used, rpm, and trim. I am most interested in figuring out how it determines fuel used, and how accurate it is. Does this unit use some kind of sensor and sending unit from the fuel tank, or is it based off some mathematical calculation of my engine size, rpms, etc.? If it's based on a calculation, it seems like I should fill the tank (55 gallons), reset the fuel used, then check the reading against how much fuel it takes to fill it the next time I fuel up, and I can have some idea of how accurate it is.
Thanks in advance!