The electronic–hydraulic analogy (derisively referred to as the drain-pipe theory by Oliver Heaviside) is the most widely used analogy for "electron fluid" in a metal conductor. Since electric current is invisible and the processes at play in electronics are often difficult to demonstrate, the various electronic components are represented by hydraulic equivalents. Electricity (as well as heat) was originally understood to be a kind of fluid, and the names of certain electric quantities (such as current) are derived from hydraulic equivalents. When taught well, the water analogy is of great use in teaching and in describing basic aspects of electric current. When taught poorly, it misleads more than it teaches. Like all analogies, it demands an intuitive and competent understanding of the baseline paradigms (electronics and hydraulics).