Yamaha Fuel Management w/ Triple F225's

I recently purchased a Triton 351CC w/ trip F225's. She has 2 fuel management gauges and 3 flow sensors. At 4000 RPM / 32kts, one gauge reads around 10gph and the other reads around 4gph.
1. I wish these were true numbers, but I doubt it. Any suggestions for getting accurate fuel burn reading?
2. How can I determine if one gauge is reading 2 motors and the other is reading 1 motor, or is one guage supposed to be showing the total of all 3?
3. Is it possible to total all 3 on one gauge?

Capt. Marc

[boats.net]

Yes one of the meters is probably connected to two engines, on bottom left corner of gauge there will be a P S displayed if Reading both engines, you can push the set button to show either P(port) or S(starboard) engine.
The gauge is only capable of reading up to two engines.