Biorhythm
Biorhythm counts whole days from the date of birth and reads three sine waves. It needs no birth time, place or ephemeris.
| Cycle | Period | Value on day t |
|---|---|---|
| Physical | 23 days | 100 × sin(2πt ÷ 23) |
| Emotional | 28 days | 100 × sin(2πt ÷ 28) |
| Intellectual | 33 days | 100 × sin(2πt ÷ 33) |
The formula is the one in Cleve Moler's MathWorks post on biorhythms. The day of birth is day 0.
What the evidence says
Controlled studies have not found that biorhythm predicts events. Hines (1998), "Comprehensive review of biorhythm theory", Psychological Reports 83, 19–64 is the review usually cited. Every reading returns a note that says this. Keep it visible in your product, and do not use biorhythm for safety, medical or hiring decisions.
Critical days
A cycle crosses zero every half period. With 23 and 33 days that can fall between two dates, for example at day 11.5. We call a date critical when a crossing falls between its start and the start of the next date, so day 11.5 marks day 11. This rule is a convention. Other charts may mark the next date as well. crossing_day gives the exact point, so you can apply your own rule.
Compatibility
Two people's waves stay the same distance apart for life, so /v1/biorhythm/compatibility takes no date. Each score is 50 × (1 + cos(2π × days apart ÷ period)): 100 when in step, 0 when exactly opposed. This scale is our convention, and the response labels it so.
Language and data
Set lang to hi for Hindi names, meanings and notes. The dates of birth are used for the response and not stored.