If two panchangs disagree by a day, the most common explanation is not that one is wrong. It is that they belong to different computational traditions.
Vakya
Vakya panchang computes planetary positions from mnemonic formulae inherited from classical texts — the Vakya system encodes positions as memorable phrases. It requires no telescope and no ephemeris, which is precisely why it survived for centuries. It remains in use in parts of Tamil Nadu and Kerala.
The formulae approximate. Over centuries, small errors accumulate, so vakya positions can drift measurably from observed positions.
Drik
Drik — literally "observed" — computes positions from modern astronomical models, which today means an ephemeris. Where vakya and drik disagree, drik matches what you would see if you looked.
Most contemporary panchangs, including ours, are drik. We compute sidereal positions with Swiss Ephemeris under the Lahiri ayanamsa.
Which is correct?
This is the wrong question, and it is worth being direct about that. Drik is more astronomically accurate. Whether astronomical accuracy is the criterion is a question about religious practice, not arithmetic, and a calendar API is not the right authority to settle it.
A community that has observed vakya reckoning for generations is not making an error that needs correcting. It is following a different tradition.
How we handle it
Our engine is drik, and we say so plainly rather than implying universality. Where traditions differ, the architecture represents the difference as a rule pack rather than resolving it silently in code — two rows, not one row with a branch in it.
What this means for your application
If your users span regions, expect disagreement with local almanacs in some years, and design for it. Surfacing the derivation — which rule, which authority, which overlap — turns "your app is wrong" into a conversation about which tradition applies. That is a much better conversation to be having.