Tach or engine synch?

[Boat Hound]

Just getting the feel for my new ride and whereas this is my first twin, I am trying to figure out if I should believe the tach or the engine synch gauge on the fuel flow - there seems to be a diff of about 100 rpms when the gauge says synch-

They are F225's 2004

 

[SenseiPSK]

Synch by ear and see which gauge is closest.

 

[JeffN]

+1 Don't have outboards but when I had my twin I/Os it was very apparent when they were in sync. Loved that sound. Listen and then check the gauges.

 

[ElyseM]

the "synch" should be accurate. the gauge would have rounding in it. you should be able to hear it as others have said. ron