important question regarding residual
 

Dear All

I would like to ask, how much a residual might be, i know that it totally depends, but I want to decide about my simulation,
on the other hand seems it is hard to get residual less than 10^-3,
i am simulating a pipe with a branch, all the b.c. are static pressure,
it is steady state simulation but in next stage i simulate a two phase flow with unsteady regime,
reynolds around 1200, laminar flow,
again i would like to know whats is the rule to define approperiate residual, either of my case and in general..

thank you so much
Hamid

this question is still very important for me :)
thanks