If this process is repeated for all possible atom pairs:

two kinds of peaks are obtained: a large peak at the origin of the unit cell which is a superposition of all the vectors between a Br atom and itself (zero-length vectors) and two peaks that represent the “forward” and “reverse” vectors constructed between the two Br atoms in the unit cell (i.e., one of those smaller peaks is due to the Br1-Br2 vector, the other is due to the Br2-Br1 vector). In a centrosymmetric unit cell of this type, for a Br1 atom at (x, y, z), there is a Br2 atom at (-x, -y, -z). Thus the two Br-Br vector peaks are at (2x, 2y, 2z) and (-2x, -2y, -2z).