there is a mistake in population balance manual
 

there must be a mistake in population balance manual,
alpha = C_VOF(cell,thread);
rho_d = C_R(cell,thread);
if thread points to secondary phase, rho_d = C_R(cell,thread) will be density of secondary phase. but in the expression it is density of first phase.....

and i do not understand the sentence "pointer to the secondary phase thread associated with d_1"...who can tell me what it mean.