You don't need a meter to set proper trim.
Total trim throws are are a matter of prefference with a manufacturers suggested base.
If you have dual servos on any control surface and use the same servo on each and the same holes on the horns, as long as they are both centered they will move equal distances on stick input. Further if you are using a Y harness to connect the 2 servos there is precious little you can do about it anyway.
You are more likely to require any trim adjustments in flight due to the airframe itself.