Pitra Dosha is read from afflictions to the Sun, to the 9th house and to the 9th lord - the significators of the father, of fortune and of the forefathers. This calculator tests your chart against each of the classical conditions, lists the ones that fired by name, grades the severity, and shows what the shared cancellation canon does to that grade.
Rather than returning a single yes or no, the calculator runs a list of named conditions and reports each one it finds. The Sun conjunct Rahu in the 1st, 5th, 7th, 9th or 10th house. The Sun conjunct Saturn. Rahu in the 9th house, or Ketu in the 9th. The 9th lord placed in a dusthana, that is the 6th, 8th or 12th. The Sun debilitated in Libra.
It also checks aspects to the 9th house, using classical graha drishti rather than a flat opposition. Every graha aspects the 7th from itself; Mars additionally aspects the 4th and the 8th; Saturn additionally the 3rd and the 10th; Rahu is taken to aspect the 5th, 7th and 9th. A malefic that aspects the 9th without occupying it therefore still registers.
The 9th bhava is the house of the father, of dharma and of the forefathers, and the Sun is the karaka, the natural significator, of the father. Pitra Dosha is the case where both of those are under pressure at once, which is why the conditions above cluster around them rather than around any single planet.
This is a structural reading, not a prediction about your family, and the page keeps to that. What the tool can state exactly is which condition is present in your chart, in which house, and how many of them there are. What follows from it is a matter for the tradition and for the remedial literature, and the page points you to those rather than making the claim itself.
The grade runs None, Low, Mild and High, and it is reported twice: once before the shared parihara canon is applied and once after, so the effect of the relief is visible rather than baked into a single number. Pitra Dosha has no cancellation clause of its own in the sources this app can name, which is exactly why the general canon is the operative one here.
The remedies most often prescribed for it are calendrical rather than gemmological: Shraddha and Tarpan performed for the ancestors, particularly during Pitru Paksha, and the associated charities. The Shraddha tool on this site computes the correct tithi for a given date of passing, which is the practical next step from this page.
For educational purposes. Astrological interpretations are traditional and not a substitute for professional advice.