The (most common) theory of biorhythm states that our daily lives are significantly affected by simple rhythmic cycles. When we are born, three cycles begin from zero point and then oscillate between -100 and 100 till we die. The physical period is 23 days long, emotional 28, and intellectual has period of 33 days.
Beware of days when any curve crosses zero especially if two or three do this simultaneously. This tool will find the three sinusiodal curves (ranging from -100 to 100):