The Dashamsa (D-10) divides each 30° zodiac sign into 10 parts, then assigns each part a zodiac sign under a stated rule. Each part spans 3°. It is derived from the same birth longitudes as the D-1 chart; it is not a second observation of the sky.
The sign-assignment rule
For an odd-numbered zodiac sign start from that sign; for an even-numbered sign start from the ninth sign counted inclusively. Count the segment number forward from that starting point. Odd and even refer to Aries as 1, Taurus as 2, and so on—not the sign’s element.
For a degree d within a sign, the segment number is floor(d × 10 ÷ 30) + 1, with d at least zero and less than 30. Here “floor” means discard the fractional part. Count the starting sign as one. Keep sign assignment separate from interpreting what a planet means.
Worked example
At 8° Aries, a planet lies in segment three, covering 6° to less than 9°. Starting at Aries, the third sign is Gemini. At 8° Taurus the start is Capricorn, the ninth from Taurus, and the third sign is Pisces. This identifies a D-10 sign; it does not establish the D-10 house until the divisional ascendant has also been calculated.
These are invented longitudes for teaching the calculation, not a client’s chart or a claimed life outcome. Self-check: 22° Cancer gives segment 8, because floor(22 × 10 ÷ 30) + 1 = 8. Cancer is sign 4, an even sign, so the start is the ninth sign counted inclusively, Pisces; the eighth sign from Pisces is Libra. For an odd-sign check, 22° Gemini starts at Gemini and the eighth sign is Capricorn.
What it is used for
Dashamsa is traditionally used for professional roles and public activity. A chart cannot determine which job offer will be made, a salary level or whether a business will survive. Reading it with the D-1 tenth house is a convention within Jyotish, not independent evidence about employment prospects.
Birth-time sensitivity
The divisional ascendant can change when the underlying ascendant crosses a segment boundary, and a D-10 segment is 3° wide. The ascendant moves about one degree every four minutes on average, so that is very roughly twelve minutes of birth time. The real rate varies with latitude and sign, so treat this as an order of magnitude, not a tolerance. If the birth time is approximate, calculate at both ends of the plausible range and note which career-chart placements change.
A reading exercise with boundaries
For a career comparison, make two columns: chart symbolism and observable requirements. Put a supposed leadership theme in the first; put actual responsibilities, skills, working hours and feedback in the second. Use the second column to evaluate an opportunity. The example calculation is an arithmetic lesson, not a recommendation to change jobs.
When two tools disagree, compare birth time and time zone, zodiac/ayanamsha, degree precision and the division rule before comparing interpretations. A one-degree difference between two ayanamshas is about a third of a D-10 segment, so a planet within a degree of a boundary can change sign between tools. More decimal places do not repair an uncertain birth record.
Sources and related guides
Calculation reference: Brihat Parashara Hora Shastra, chapter 6, the section describing the sixteen divisions. The cited text documents the traditional scheme; it does not validate personal predictions. Our examples above show the arithmetic without reproducing the text’s promised outcomes. For context read what divisional charts are and how to compare them.