Biorhythms (生物節律)

The Seventies' Favorite Chart — Served With the Verdict

Overview

Three sine waves anchored to your birthday: a 23-day physical cycle, a 28-day emotional cycle, a 33-day intellectual cycle — crossing zero on 'critical days' when, the theory said, you were accident-prone and off your game. Biorhythms were the 1970s' favorite personal chart, printed by mall kiosks and pocket calculators, consulted before flights and exams. askTIAN serves them with something no biorhythm calculator ever includes: the verdict. This is the one system in the catalogue whose claim has been directly tested by controlled studies — and refuted. The provenance note saying exactly that ships on every response, verbatim, beside mathematics that is otherwise exact to the day. A retro pastime, done with the catalogue's full honesty rail: real arithmetic, disclosed provenance, and never a word of health, safety or performance advice.

Origin & history

The cycles began in 1890s Berlin and Vienna: Wilhelm Fliess — Freud's closest correspondent — proposed the 23-day 'male' and 28-day 'female' periods, Hermann Swoboda arrived at similar numbers independently, and a 33-day intellectual cycle was added by later hands. The theory slept for decades and woke in the 1970s as a craze: bestsellers, newspaper columns, dedicated calculators, corporate safety programs in Japan plotting workers' critical days. A fourth, 38-day 'intuitive' cycle was bolted on during the boom — this endpoint carries it as exactly that, an add-on, off by default and labelled. The arithmetic is the whole system: value equals the sine of two-pi times days-since-birth over the period; a critical day is a zero crossing; nothing else is computed because nothing else was ever specified.

Then science did what it rarely gets the chance to do with divination: the claim was specific enough to test. Fixed periods, birth-anchored, predicting performance and accidents — controlled studies through the late 1970s and 1980s checked accident records, sports results and exam scores against the cycles, and found nothing beyond chance. No peer-reviewed replication supports the theory; the scientific literature closed the question. askTIAN's provenance registry — the same one that discloses Human Design's 1987 origin and the Celtic Tree Calendar's 1948 authorship — carries the biorhythm entry with the refutation stated plainly, and every API response serves it. What remains is what was always genuinely there: elegant arithmetic, a pleasing chart, and a period piece of twentieth-century pop mysticism worth having in a complete catalogue — as history, honestly labelled.

How it works

Send a birthdate and a date. The engine computes days-since-birth on UTC calendar days and evaluates each cycle exactly: sine of two-pi t over 23, 28 and 33 (and 38 if the add-on is requested). Today's block gives each cycle's value, percentage, phase — high, low, or critical at the zero crossings — and the days until its next critical day. A chart of up to sixty-one days, centred on the date, carries per-day values and critical flags, ready to plot as the classic three-wave graph. A partner's birthdate adds the classic compatibility layer: the offset between births reduced modulo each period — one hundred percent in phase, zero in antiphase, symmetric by construction. The test suite locks the arithmetic as theorems: all cycles critical at zero on the day of birth, exact periodicity, the quarter-period peak, zero-crossing detection, and identical-birthday hundred-percent compatibility. Every cycle's meaning field says 'per the tradition' — the engine reports what the theory claimed, and asserts none of it.

Good for

Use cases

The Retro Chart

Render the three sine waves over a month, critical days ticked — the mall-kiosk chart of 1976, pixel for pixel, with the provenance note as its caption.

The Honest Widget

A daily 'your cycles today' card that includes the disclosure — the rare pop-mysticism feature a serious product can ship without wincing, because the verdict is on the label.

Couple Compatibility, Seventies Edition

The classic birth-offset percentages beside the catalogue's real synastry endpoints — the retro number and the serious readings, clearly told apart.

Critical-Thinking Classroom

The one divination system with a controlled-trial literature: chart it, read the provenance note, and discuss what made the claim testable — a ready-made lesson.

Key terms

The Three Cycles
Physical (23 days), emotional (28), intellectual (33) — sine waves anchored at birth, per the tradition governing stamina, mood and mind. The engine reports the claims as claims.
Critical Day
A zero crossing — the cycle switching sign — when the theory held one unstable. Flagged per cycle and per chart day.
The Intuitive Cycle
The 38-day fourth wave bolted on during the 1970s boom — available, off by default, and labelled the add-on it is.
Birth-Offset Compatibility
The classic percentages: the gap between two birthdays reduced modulo each period — 100% in phase, 0% in antiphase, symmetric by construction.
Refuted, and Said So
Controlled studies tested the predictive claim and found chance — the provenance registry's strongest note, served verbatim on every response.
Per the Tradition
Every meaning string in the response is prefixed by the engine's stance: what the theory claimed, reported — never asserted.
UTC Day Arithmetic
Days-since-birth on UTC calendar days — the one convention choice, stated, so charts reproduce identically everywhere.
The Honesty Rail
The same provenance standard that dates Human Design to 1987 and the Celtic Tree Calendar to 1948 — applied here to the system with the clearest verdict of all.

API

The askTIAN Biorhythm API computes the 23/28/33-day cycles exactly — today's values with phases and next-critical countdowns, a centred plotting-ready chart of up to 61 days, the optional 38-day add-on labelled as such, and the classic symmetric compatibility percentages — with the catalogue's strongest provenance note served verbatim on every response: a modern invention whose predictive claim controlled studies have refuted, offered as a retro pastime and never as advice. The arithmetic is test-locked as theorems. Pure compute, no LLM, 1 TIAN — the catalogue's cheapest chart.

Endpoint: POST /trpc/biorhythm.chart — 1 TIAN Points. See the API documentation and Playground.