The Dwadasamsa is the twelfth divisional chart: each sign of 30 degrees is cut into twelve parts of 2 degrees 30 minutes, counted forward from the occupied sign itself. Brihat Parashara Hora Shastra ch. 6 assigns the D12 to parents and ancestry, and it is read alongside the 4th and 9th houses of the birth chart.
The D12 has the simplest counting rule of the middle divisions: no modality test, no parity test. Twelve parts of 2 degrees 30 minutes, running forward from the sign the planet occupies. A planet at 0 to 2 degrees 30 minutes of Leo stays in Leo, from 2 degrees 30 minutes to 5 degrees it is in Virgo, and so on around the zodiac once.
Because the twelve parts map onto the twelve signs in order, the D12 has an unusual property: it turns a planet's degree within a sign directly into a sign-count. A planet exactly halfway through its sign lands in the 7th from it, which is the opposite sign, in every case.
The subject BPHS assigns is parents and lineage, so the division is read against the two bhavas that carry that subject in the birth chart: the 4th for the mother and the 9th for the father, with the Moon and the Sun as the corresponding natural significators. The D12 refines what those houses already say.
It is also one of the divisions where the comparison across charts matters most, because a parent's own chart is often available. Reading the D12 of one chart beside the D1 of another is beyond what a single-chart page can do, and it belongs to a full consultation rather than to a calculator.
A dwadasamsa is 2 degrees 30 minutes wide, and the ascendant covers that in about ten minutes on average, so the D12 lagna needs a birth time accurate to a few minutes. Planetary positions in the division are far more stable than the lagna: the Moon, the fastest graha, takes about four and a half hours to cross a dwadasamsa.
AstroZivi names the subject BPHS gives the chart and stops there. It does not print a reading about your parents from a placement, because that step needs a text and a verse behind it. What the page states exactly is the D12 sign, house, degree and dignity of each graha.
For educational purposes. Astrological interpretations are traditional and not a substitute for professional advice.