English: Plotted on the top right, the surface potential (ψo) propagates outward into the cloud of ions treated as point charges immersed in a solvent with a constant relative dielectric. The zeta potential (ζ) is located at the slip plane, which is proposed to coincide with the hydrodynamic radius (Rh). Rp is the protein radius and κ-1 is the Debye length.