Resistive pulse sensing (RPS) is the generic, non-commercial term given for the well-developed technology used to detect, and measure the size of, individual particles in fluid. First invented by Wallace H. Coulter in 1953,[1] the RPS technique is the basic principle behind the Coulter Principle, which is a trademark term. Resistive pulse sensing is also known as the electrical zone sensing technique, reflecting its fundamentally electrical nature, which distinguishes it from other particle sizing technologies such as the optically-based dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA). An international standard has been developed for the use of the resistive pulse sensing technique by the International Organization for Standardization.[2]