The three cycles
The intellectual cycle is the longest of the three, 33 days. It was the last to be proposed, in the 1920s, and the theory says it governs concentration, memory and judgement.
33days
The theory assigns the intellectual cycle thinking: concentration, memory, learning and decisions. The high phase is read as a time for study and for choices that need a clear head, the low phase as a time to review rather than begin, the critical days as absent-minded. Of the three cycles it is the one that was added by observation of students rather than patients.
The intellectual cycle begins on the day you were born and repeats every 33 days. To find where it sits on any date, count the days since your birth, divide by 33, and the remainder is the day of the cycle; the day you were born is day 1. That is the whole calculation, and it is the same for everyone.
Step by step, with a worked example: How to calculate a biorhythm.
Eight states
The symbols and their meanings are explained on How to read a biorhythm chart.
Day 1
Critical, turning up
Days 17–18
Critical, turning down
Day 1, when the cycle begins and rises through its midline, and the day about half-way through, when it falls below it. The theory reads both as unsettled rather than bad: days to notice how you feel. Critical days, explained.
BioCalendar
In BioCalendar the intellectual cycle is drawn in blue. Goals about focus or learning use it to mark the stretches of the month above the midline, and the Companion will tell you where it sits if you ask about a day you want to think clearly on.
The record
Studies that looked for this cycle in the things it is said to govern did not find it. We set out the research on Are biorhythms real?, and we ask you to read the cycle the way BioCalendar presents it: as a counted pattern, and a prompt to notice the day, not a forecast.
