In this article, the following conventions and definitions are to be understood:
* The Reynolds number Re is taken to be Re = V D / ν, where V is the mean velocity of fluid flow, D is the pipe diameter, and where ν is the kinematic viscosity μ / ρ, with μ the fluids Dynamic viscosity, and ρ the fluids density. 
* The pipes relative roughness ε / D, where ε is the pipes effective roughness height and D the pipe (inside) diameter. 
* f stands for the Darcy friction factor. Its value depends on the flows Reynolds number Re and on the pipes relative roughness ε / D.
* The log function is understood to be base-10 (as is customary in engineering fields): if x = log(y), then y = 10.
* The ln function is understood to be base-e: if x = ln(y), then y = e.