This is an elusive subject with added order of magnitude. If that doesn't make sense, well... It tells that I'm confused. Say rate of fluid flow in a uniform cross-sectional area pipe |A|=L^2,|R|=L^3*T^-1. Is it customary that I get all variebles to the same order of magnitude and be able to express it as the normal equation d^2*V for fluid flow rate?