Usually engine synchronizers are a separate guage what it does is beats the ignition pulses against each other from each engine, thus and difference is seen as not synchronized. Normally on smaller twin engine boats you bring the engines up to speed and once trimmed and settled in back one or the other engines off so the neddle stays in the center. What this means is the the ignitions pulses are compared against each other and the difference is displayed as one engine is a little ahead in RPM than the other. It makes no sense to try and synchronize the engines as you are coming up to cruise, there is just to much happening! Syncronizing happens after everything else is settled down and you are on a straight course heading to where ever. If you set the synchronizer and make a turn you will not that the inside engine will loose RPM while the outside engine will gain RPM after the turn is completed and every thing is settled back down the engines should come back into synchronization.
I know this is a pretty simple and long explaination but it seemed that some of you did not know what a Synchronizer was or how to use it.. Yes usually Synchorizers are more accurate than most tachometers because they are comparing the ignition pulses of the engines. I would tend to believe a synchrometer before I would believe engine Tachometers.
Although I have a synchronizer on my boat after many years boating I have an ear for how the engines sound and can hit the synchro point almost every time!
Mike -
