[Tuomas Nylund] wanted a way to visualize the electromagnetic fields (EMF) around him ... to the probe and should not be used for serious measurements. But we think he’s selling himself short.

Voltage is a measure of energy, and energy is always conserved. So the EMF \(E\) of a cell is equal to the sum of its terminal potential difference, \(V_{tpd}\), and the lost volts, \({V_L}\).