Twenty portions, three starting signs
Viṃśāṃśa, also spelled Vimshamsha or Vimsamsa, is the twentieth divisional chart in Jyotish. A sidereal rāśi spans 30°. D20 divides it into twenty equal 1°30′ portions. The first portion of a movable sign counts from Aries, of a fixed sign from Sagittarius, and of a dual sign from Leo. Each following portion advances one sign through the zodiac. This is the Parāśari rule in chapter 6, verse 17; another varga convention can give different results.
The calculator applies that rule to this website's independent sidereal D1 positions. The D1 calculator uses Astronomy Engine 2.1.19 and an approximate Lahiri ayanamsha, with the seven classical grahas and mean Rahu and Ketu. It asks for the historical UTC offset because the form does not infer time-zone history from a place name.
Reading the result
Each row keeps the source D1 sidereal sign and degree beside the derived D20 position. It identifies the numbered 1°30′ portion and the Aries, Sagittarius, or Leo starting sign. The South Indian diagram fixes signs in place and marks the transformed Lagna. A placement within 0.05° of a boundary is flagged, since a small change in input can move it to another D20 sign.
The D20 degree expands a 1°30′ interval to a 30° coordinate. It is a calculation reference, not a newly observed sky position or a measurement of spirituality. Compare the result with the D1 rāśi chart and read the D20 method guide before comparing it with a chart from another provider.