Gen. 1 Module block numbering and module paring etc.

Having a hard time finding any information on the Gen 1 packs. It’s been a while and I just want to make sure I match the modules up correctly. Do the block numbers count down from the ECM (19-1)? Is the voltage drop, measured by the ECM, between the pair in each individual block or between neighboring blocks (or am I completely off on this)? How much voltage drop is ok before the ECM throws the triangle? Anything else that might be helpful is welcome