Two reference frames
Astronomical software can express a position relative to the moving seasonal equinox, usually called tropical longitude. A sidereal chart applies an offset called an ayanamsa to express that position in a different zodiac reference. The formula is simple in outline—normalize the tropical longitude minus the offset—but the chosen offset and astronomical conventions matter.
A sign is 30° wide. Changing the offset by even a small amount can change the sign or nakshatra of a placement near a boundary. This does not mean one user entered the wrong birth date; it may mean the two tools are using different definitions.
What Kalika calculates today
The current beta uses Astronomy Engine for apparent geocentric planetary positions and a compact Lahiri-style precession approximation anchored at J2000. It is labelled approximate because it is not an implementation of the full Swiss Ephemeris Lahiri mode. The displayed offset and engine label are part of the result, not hidden settings.
A small set of independent comparison fixtures checks ascendant, Sun, and Moon values across multiple dates. Those checks are useful, but they do not prove agreement for every date, latitude, body, or boundary. This is why the result remains a calculation beta.
A fair comparison checklist
To compare two charts, use the same birth instant, coordinates, sidereal method, node convention, and house system. Compare raw degrees before interpreting a difference in sign labels. If one site shows a cusp-based house chart and the other shows whole-sign houses, the planet longitude can agree while the house number differs.
If you report a discrepancy, include the settings and the placement in question—but do not post a real person’s full birth details publicly without their consent.