Where the numbers come from.

Planetary longitudes are computed with Skyfield against JPL DE440s, the same ephemeris kernel used for spacecraft navigation. It is a 32 MB binary of Chebyshev coefficients covering 1849 to 2150, and it is fetched at setup rather than committed.

This is the difference between an answer and a lookup. A date-based approximation puts the Sun in about the right sign; it cannot tell you the Moon’s nakshatra, and six of the eight compatibility kootas are read from exactly that.

Indian astrology measures from the fixed stars; Western astrology measures from the spring equinox. The Earth’s axis wobbles, so the two have drifted apart — about 24° today. That offset is the ayanamsa, and it changes by roughly 50 arcseconds a year, which means it is a function of the birth date and not a constant.

Lahiri is the default because it is what the Indian government’s calendar reform committee adopted and what most Indian practice uses. Raman and the two Krishnamurti variants are also available. The value actually applied is printed on the chart and in the report, so you can check it.

A wall clock reading is not a moment in time until you know the offset that was in force at that place on that date. India has not always been on +05:30: before 1906 much of it kept Madras Mean Time at +05:21:10, and during 1942–45 the country ran an hour ahead on +06:30.

Resolution runs server-side against the historical zoneinfo rules rather than in your browser, because a browser’s time-zone database is not guaranteed to carry transitions that old. The chart page shows you the whole chain — wall clock, zone, UTC instant, Julian day — before it computes anything.

Where a local time is genuinely ambiguous, which happens for one hour each year in any place that observes daylight saving, we ask rather than guess. A time that never existed is refused outright.

Prose is generated against a fact sheet extracted from your chart, then passed through a validator before it can be printed. The validator rejects a draft that names a year, a degree, a planet or a sign that is not in the chart, and it rejects language that predicts death, names an illness, or guarantees an outcome. A draft that fails is retried once and then replaced by deterministic text.

One detail from building it, because it says something about the care required: the harmful-language check has to mask the astrological vocabulary first, since Cancer is both a sign and a disease.

It is not a prediction of events. It describes placements, periods, and what those are traditionally read to favour — which is a claim about a tradition, not a claim about your future.

It is not medical, legal or financial advice, and it will not be made to sound like any of them. Where a chapter cannot be computed, it is left out rather than filled with something plausible.