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.
And a charley horse can occur at any time of the day or night. People who are obese are more likely to experience charley horses because of poor circulation in their legs. Athletes often experience charley horses because of muscle fatigue or overuse.