Designing a duct system

So recently I was tasked with designing a duct system for a small dental practice. I learnt a few things that bear repeating. The terminals where ceiling diffusers, so I set about selecting them, looking for which sizes would best suit my flow rates. However I ignored the fact that at these differing flow rates, the diffusers would have to be adjusted to varying pressure levels. Now in a system where all the terminals have balancing dampers, its OK for you to have differing pressure drops in your diffusers, but as was pointed out to me, if I have a diffuser in one room with a low pressure drop, and another in the next room with a high pressure drop, the flow of air will tend towards the lower pressure, and your flow rate there will increase, while your flow rate in the other diffuser will decrease. Thus when designing a system, it is important to insure that all your terminal outlets have similar pressure drops, unless there are individual balancing dampers at each outlet.