How this panchangam is checked

Astronomy is reproducible from the ephemeris. Rules are traced to a text, named by passage, and checked against published days.

Two kinds of statement appear in a panchangam, and they are checked in two different ways.

Computed values

Sunrise and sunset, the five limbs and their boundaries, the moon sign, the solar date, the lunar month and the era counts come from the Swiss Ephemeris under the Lahiri ayanamsha, at the horizon of the town in question.

These are reproducible. Given the same place, the same instant and the same ayanamsha, anyone with the ephemeris gets the same numbers. That is the test they have to pass.

Rules

An observance date is not computed; it is decided, by a rule a tradition wrote down. So the test is different: we trace the rule to its text, quote the passage, and name the page it sits on.

Pradosham carries the Dharmasindhu's clause on the trayodashi. Ekadashi carries both vedhas. Yajur Upakarma carries the Calendar Reform Committee's criterion and the Dharmasindhu's reading side by side, because the two texts do not agree.

Then against practice

A rule that is correctly transcribed can still be wrongly implemented, so each one is run against days the established almanacs have already published. Our pradosham, sankashti, shivaratri and ekadashi rules reproduce the published days for September and October 2026, including the days where the Smarta and Vaishnava reckonings separate.

Agreement is a check rather than a proof, which is why the passage itself is printed on every rule page: the reading is there to be examined.