Biorhythms

A Biorhythm is a hypothetical cycle in physiological, emotional, or intellectual well-being or prowess. "Bio-" pertains to life and “rhythm” pertains to the flow with regular movement. The theory has no more predictive power than chance, and has been labeled a pseudoscience by skeptics.
Having said all that I have been using biorhythm charts ever since I discovered them in the 1970’s and found them most useful.
The theory of biorhythms claims that one's life is affected by rhythmic biological cycles, and seeks to make predictions regarding these cycles and the personal ease of carrying out tasks related to the cycles. These inherent rhythms are said to be composed of three cyclic rhythms: the physical, (23 day), emotional (28 day) and the intellectual (33 day) cycles.
The three classical cycles of biorhythms are often represented graphically in a sinusoidal waveform. Each cycle oscillates between a positive phase [0%..100%] and a negative phase [-100%..0%], during which biorhythmic activity strengthens and weakens. The waveforms start at the neutral baseline (0%) at the time of birth of each individual. Each day that the waveform again crosses this baseline is dubbed a critical day, which means that tasks in the domain of the cycle are far more erratic than on other non-critical days. The purpose of mapping the biorhythmic cycles is to enable the calculation of critical days for performing or avoiding various activities.
Years ago I used to have a whole year printed out but now thanks to the internet I can see my biorhythms on a daily basis. Here is the site I use http://www.bio-chart.com/.