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Biorhythms are theoretical cycles which allegedly dictate health and behavior. The name is evocative of circadian rhythms, the difference being that circadian rhythms are based on scientific observation, while biorhythms are pure pseudoscience.
Due to its origins, the theory of biorhythms can be considered a first cousin of numerology.
The original theory was dreamed up by Wilhelm Fliess (1858-1928), who played with mathematics and eventually came to the conclusion that everything could be tied back to the numbers 23 and 28. He decided that these referred to bodily cycles, which he dubbed "male" and "female" respectively. Years later, Professor Alfred Teltscher added a third 33-day cycle and renamed the three cycles physical, mental and emotional. Thus, the theory of biorhythms was born.
Since the development of the original theory, many additional cycles have been submitted, including intuitional, aesthetic, spiritual, passion, wisdom, mastery, gullibility, tragedy, comedy and tastiness. However, the vast majority of biorhythm technicians focus on the core cycles: The 23-day physical cycle, the 28-day emotional cycle and the 33-day mental cycle.
It's good when a cycle is above the baseline and bad when it is below the baseline. That is, unless a particular reading looks wrong, in which case it's good when a cycle is moving upward and bad if it's heading downward, regardless of position. Even if you were at a pessimistic period where all cycles were below normal and heading downward, it only happens in rare cases and will quickly rebound after a few days. So basically a biorhythm chart can say anything at all.
As with other charts that use one point of reference (in this case, the date of birth), the same chart can be recycled for other people.
 Actual "biorythms"
Women, as most people know, experience periodic fluctuations in emotions known fearfully by men as "that time of the month". Some scientists speculate that men may experience similar, though less severe, hormonal cycles as well.
- ↑ Biorhythms — Skeptic's Dictionary
- ↑ Some of those may be fictional.
- ↑ As of 1 Dec 2016, Google Play store had more than 100 apps and popular download site CNet listed 125 programs.
- ↑ Convergence VII: Casio Biorhythm Calculator, Retrothing May 2006
- ↑ See the Wikipedia article on Biorhythm.
- ↑ Men's Moods Demystified, Psychology Today (IWBM)
- ↑ The Male Period