To be absolutely 100% correct in all cases, the full CG calculation should always be made of course, however on two types I have conducted extensive base training/circuits on , using a default figure of 2 units NU stab trim (767) or 4 units NU stab trim (757) has always produced an in-trim airplane for the take off phase 99.9% of the time.Actually 100% of the time.PETER