The frustration
Two apps, same birth date and time and place, two different charts. A planet that sits in Scorpio in one app appears in Libra in another. A planet that falls in the seventh house under one calculation is in the sixth under another. Which one is right?
Usually, both. They are correct calculations of different settings. Understanding which setting produced which difference is the diagnostic skill that makes chart comparison useful rather than confusing.
The six common sources of disagreement
1. Zodiac: tropical vs sidereal
This produces the most dramatic differences. The tropical zodiac begins at the March equinox; the sidereal zodiac is anchored to the fixed-star background. The two starting points are currently about 23–24 degrees apart and diverge by about one degree every 72 years because of a celestial wobble called precession.
A planet at 5° tropical Pisces falls at roughly 11° sidereal Aquarius. That is a sign change. If one app uses tropical and another uses sidereal, every sign placement in the chart will differ — Sun, Moon, Mercury, Venus, all of them. This is not an error. It is a choice of zodiac. Veyra uses the tropical zodiac throughout.
The essay explains both systems and why switching positions between them without also switching interpretive traditions is a category error.
2. House system
The zodiac signs are fixed — the same in every chart under the same zodiac. The houses are not. They are calculated by one of several competing mathematical methods, and the choice of method can move a planet from one house to another.
Placidus (Veyra's default) divides the sky based on the time a degree takes to travel from the horizon to the meridian. Whole Sign assigns the entire sign containing the Ascendant to the first house, the next sign to the second, and so on. Equal House spaces cusps thirty degrees from the Ascendant. Koch uses yet another division. A planet near a house boundary may fall in different houses under different systems.
Crucially: house system changes never affect sign placements. If your Sun is in Scorpio under Placidus, it is still in Scorpio under Whole Sign. Only the house shifts. The essay covers the major options and when the choice matters.
3. Time zone and daylight-saving handling
Most apps calculate time zone from the birth location automatically, but older records, historical time zone data, and unusual locations can introduce errors. Daylight-saving time status is a particular source of trouble: in some regions and eras, the records are ambiguous. If an app applies daylight saving when it should not, the chart is cast for a time one hour off, shifting fast-moving bodies like the Moon and the Ascendant significantly.
When charts disagree and you suspect a time zone issue, check whether both apps are using the same UTC offset for the birth location and date.
4. Birth time precision
The Ascendant moves through roughly one full degree every four minutes. An uncertain birth time — or a time rounded to the nearest half hour by a hospital record — can place the Ascendant in the wrong degree and shift every house cusp accordingly. The Moon, which moves about 12–15 degrees per day, can also change signs within a few hours.
If the birth time is recorded as "around 9 PM" rather than a confirmed clock time, treat the Ascendant and Moon sign as approximate and avoid placing interpretive weight on placements that depend on that precision.
5. True node vs Mean node
The lunar nodes — the North and South Node, the points where the Moon's orbit crosses the ecliptic — can be calculated two ways. The True Node tracks the Moon's actual orbital geometry, including small oscillations, and moves irregularly forward and backward. The Mean Node is a mathematical average that moves smoothly backward through the zodiac.
At any given moment, the two calculations differ by up to 1–2 degrees. Near sign boundaries, this is enough to place the node in different signs. This is one of the smaller sources of disagreement but worth checking when nodes are at stake.
6. Ephemeris and rounding
The underlying astronomical data — the ephemeris, a table of planetary positions over time — can also vary slightly between calculation packages. The differences are typically small (fractions of a degree) and rarely change interpretations, but at tight boundaries, they can. Veyra uses Swiss Ephemeris via pyswisseph, which is among the most precise publicly available ephemerides.
Diagnosing the difference
When two charts disagree, check in this order:
- Signs differ everywhere? → Different zodiac (tropical vs sidereal).
- Signs agree but houses differ? → Different house system.
- Moon or Ascendant in a different sign? → Time zone, daylight-saving, or birth time precision.
- Only the nodes differ? → True vs Mean node calculation.
- Everything else matches but one planet is slightly off? → Ephemeris rounding near a cusp.
Identify the setting before interpreting the result. A house placement that changes between systems is telling you something about the sensitivity of that planet's position, not that one chart is authoritative and the other is wrong.