Visual explainer
Stable layer
Astronomical positions
Choice layer
Chart conventions
Short explainer
Two astrology apps can disagree without either using bad astronomy. First match the zodiac, house system, time zone, coordinates, and lunar node setting. Then compare the exact degrees. Different settings change the chart. Matching settings should not.
What's actually true — the astronomy
Planetary longitude is the stable layer. Given the same instant, location, reference frame and ephemeris, two calculators should agree within a small tolerance. The ascendant and house cusps also depend on exact birth time and coordinates, while time-zone or daylight-saving mistakes can move them substantially. Tropical versus sidereal is a reference-frame choice; house systems are alternative geometries laid over the same planetary positions.
What the tradition says (interpretation)
Western astrologers commonly use the tropical zodiac with Placidus or whole-sign houses. Vedic astrologers usually use a sidereal zodiac with a named ayanamsa, often Lahiri, and frequently whole-sign houses. Those are distinct rule sets. Calling one output "more accurate" without first naming the system confuses a traditional choice with a calculation error.
The decision-science move — what to actually do
Compare charts like a controlled experiment. Enter the same birth time, time zone and coordinates; choose the same tropical or sidereal zodiac, ayanamsa, house system and node type; then compare the exact degrees before comparing interpretations. A trustworthy app exposes every one of those settings. If it hides them, you cannot audit why the chart changed.
Why this question is here
These current discussions surfaced the question. They are community signals, not evidence for the answer; the technical and research sources are listed separately below.
More questions like this in the decision-science library, or read how we separate the math from the myth.