Volt units in science. They chose such a ratio because the cgs unit of voltage is inconveniently small and one volt in this definition is approximately the emf of a Daniell cell, the standard source of voltage in the telegraph systems of the day. At that time, the volt was defined as the potential difference [i.e., what is nowadays called the "voltage (difference)"] across a conductor when a current of one ampere dissipates one watt of power. The "international volt" was defined in 1893 as 1/1.434 of the emf of a Clark cell. This definition was abandoned in 1908 in favor
Transepithelial potential difference Transepithelial potential difference Transepithelial potential difference (TEPD) is the voltage across an epithelium, and is the sum of the membrane potentials for the outer and inner cell membranes. The diagnosis of Cystic Fibrosis (CF) is usually based on high sweat chloride concentrations, characteristic clinical findings (including sinopulmonary infections), and/or family history. However, a small portion of patients with Cystic Fibrosis especially those with "mild" mutations of the Cystic Fibrosis Transmembrane Regulator ion channel (CFTR), have near-normal sweat tests. In these cases, a useful diagnostic, adjunct involves measuring the nasal transepithelial potential difference (ie, the charge on the respiratory epithelial surface