Parashara and most Vedic astrology use Whole-Sign houses (30° per house, starting at Lagna). KP uses Placidus, a Western house system adapted for Vedic practice.
Placidus principle: Houses are defined by time, not space. The time it takes for the ecliptic degree at the IC (Imum Coeli, midnight point) to reach the MC (Midheaven, noon point) is called the "semi-diurnal arc." This arc is divided into 6 equal time periods (from IC to MC), giving 6 cusps. The same time periods are used in reverse (from MC to IC) for the 6 opposite houses, yielding 12 unequal house cusps.
Result: Houses vary in size. At the equator, all houses are 30°. At higher latitudes (north or south), some houses shrink to 20° while others expand to 40°. At very high latitudes (>60°), houses can become extreme or even "intercepted" (a sign can fall entirely within a house, not touching either cusp).
Accuracy: Placidus requires precise birth time. A 4-minute error in birth time can shift house cusps by 1°, affecting sub-lord calculations and horary outcomes. This is why KP practitioners emphasize birth time verification.
Why KP chose Placidus: K. Krishnamurti found that Placidus cusp calculations, combined with sub-lord analysis, produced accurate event predictions in horary astrology. Classical Vedic texts use whole-sign houses; KP's adoption of Placidus was controversial but proven effective empirically.
The calculator computes Placidus cusps using Swiss Ephemeris. You will observe how house sizes vary with latitude and see why horary results can differ significantly if an incorrect latitude is used.
Time, not space. Whole-sign and equal-house systems divide space: each house is a fixed arc of the zodiac. Placidus divides time, splitting the interval between the ascendant and the midheaven into equal parts of diurnal motion. This is why Placidus houses are unequal, and why the inequality grows at high latitudes where day length becomes extreme.
The consequence for reading. Because cusps fall at particular degrees rather than at sign boundaries, a planet can occupy the sign of the 10th house while belonging to the 9th house by cusp. KP treats the cusp assignment as authoritative. This single difference accounts for much of the divergence between a KP reading and a classical one of the same chart.
The high-latitude caveat. Above roughly 66 degrees of latitude, Placidus breaks down: some houses become undefined because the required points never rise. Practitioners working with charts from far northern or southern latitudes need to know this rather than trusting whatever their software returns.
What to check first. When a KP reading conflicts with a classical one, compare the house assignments before anything else. In most cases the disagreement is not interpretive at all; the two systems have simply placed the same planet in different houses.