[ P_1 + \frac12\rho v_1^2 + \rho g h_1 = P_2 + \frac12\rho v_2^2 + \rho g h_2 ]

Where (R) is resistance coefficient and (n) = 1 (laminar) or 2 (turbulent).

Where (f) = friction factor (Darcy-Weisbach equation). This is the central principle in designing pumping systems. Differential pressure is measured using specialized devices. The most common include:

is the scalar magnitude of the difference between two absolute pressures at distinct points or regions: