Parashara and KP both use Vimshottari Dasha, which divides the 120-year life cycle into planetary periods (Sun 6 years, Moon 10, Mars 7, Rahu 18, etc.). Events are predicted to occur during those dasha periods.
Nadi uses a different mechanism: Progression. A planet at birth has a fixed degree (e.g., Mars at 18° Virgo). As time passes, other transiting planets cross that degree. When a transiting planet touches (or passes through) the natal planet's degree, an event related to that planet is triggered.
Primary progressive indicator: Jupiter. Jupiter progresses at ~1° per year (it moves ~1° per month in the actual zodiac, so over a full 12-month year, it progresses ~12°, which is simplified to 1° per year for the nadi calendar). When Jupiter reaches your natal Mars's degree (18° Virgo), a Mars-related event is predicted (action, energy, accident, surgery, or competitive victory).
Secondary indicator: Saturn. Saturn progresses at ~1° per year (inverted: Saturn causes events when native's age approaches Saturn's return or Saturn transits the natal planet). When Saturn reaches your natal Venus's degree, a Venus-related event is predicted (marriage, financial change, or separation).
This is a linear, time-based system. Unlike Vimshottari, which divides time into discrete planetary periods, progression is continuous. As time flows, planets continuously progress through degrees, and each touching triggers an event.
Simplicity and specificity: Progression makes event prediction simple. "Jupiter will reach your Mars degree at age 34; expect action/property/competition event then." No need to memorize Vimshottari dasha sequences.
Limitation: Progression is purely geometric (Jupiter at this degree → event). It lacks the logical depth of Vimshottari or Parashara's nuanced dasha interpretation. Why Jupiter touching Mars should cause an event is not explained; it is assumed as given.
The progression calculator identifies Jupiter and Saturn's progression through a native's chart and highlights touching points (conjunctions with natal planets). You will see your upcoming event windows (next 5-10 years) via progression.
The substitution. Where Parashara divides life into planetary periods calculated from the Moon's nakshatra, Nadi advances the planets forward from their birth positions and reads their contacts with natal degrees as events. There is no dasha balance, no antardasha arithmetic and no 120-year cycle.
Why Jupiter and Saturn. The two slow planets are used as clocks because their motion maps usefully onto a human lifespan. Jupiter advances at roughly a degree a year in this scheme, which lets degrees be read directly as ages. Saturn moves more slowly still and marks longer structural phases.
What a contact means. When a progressed clock reaches the degree of a natal planet, that planet's significations are activated. The nature of the event comes from the natal planet; the timing comes from the clock. This is the whole timing mechanism of the system.
The precision problem. Because a degree maps to about a year, an error of two degrees in either the natal position or the progression rate shifts a prediction by two years. Over a lifetime these errors accumulate, which is why Nadi timing claims should be read as windows of several years rather than as dates.