Since the distance between the Zeeman sub-levels is a function of the magnetic field, this effect can be used to measure the magnetic field, e.g. that of the Sun and other stars or in laboratory plasmas.
Charley horse: Slang for a cramp in a muscle in the leg, usually caused by a strain or injury. A charley horse can last anywhere from a few seconds to over a quarter of an hour. It is not uncommon for one to recur before it finally resolves.
In most of the cases, Charlie horses are the late responses of straining a muscle during exercise, or otherwise. The most common type of Charley horse, found in the calf region, is often the result of kicking while swimming. Charley horses in the upper leg are mainly caused by activities like running or jumping.