re: Measuring trees for Louisiana/National big tree registry

I know the dbh is supposed to be measured 4.5' from the ground, but there are conflicting rules when the tree forks below the traditional dbh height of 4.5'. I don't know if I would have to count it as different trees (hope not) or if I can still use the dbh from the smallest circumference below the fork, or the square of the sum of the circumferences of the individual forks.