I was gonna go to sleep, but I read something interesting.

People are born with three natural cycles:

1. A 23-day physical cycle
2. A 28-day emotional cycle
3. A 33-day intellectual cycle

The three cycles take forms of sinusoidal waves, with the peaks representing our peak ability in the corresponding department.

Further search on Google brought me to this analysis, which told me I am at the peak of my intellectual cycle, with rising physical ability while nearing the trough in emotional strength. (There are several more references and calculators if you just search for the term).

And guess where did I read about the theory of biorhythm?

An unlikely place: a grade 11 math text book.