AT&T MERLIN LEGEND Release 2.0 Programming Summary Manual page 76

System Operator Positions
Primary Operator Positions
The primary operator position is the position to which your call is directed
when you dial 0 on a System Access button.
The first jack on the first MLX module in your system is assigned as the
primary operator position.
If your system has QCC operator positions, this position must be changed
from the factory setting (DLC) to a QCC operator position. (The position of the
primary operator cannot be changed from the first jack on the first MLX
module.)
System Operator Positions
3-3