The best way I have found to do it is to mechanically trim the plane in the begining (adjusting the clevises on the control horns) after the initial trim flight so the trim levers are always set to zero. I find it takes an average of two-three trim flights before I have the plane mechanically in trim. Then when I move to a new transmitter I know the plane is basically in trim with only minor if any trim adjustments needed. This past winter I got a new Futaba 8FG and it was easy to move a number of planes over to it from my 7C Fasst system because they all were in mechanical trim.

BTW, in the days before computer radios all trim levers were mechanical and could easily moved between flying sessions so it was necessay to mechanically trim the plane if you did not want a unhappy surprise on the first flight of the day.

Bruce