Twenty-four portions: Leo or Cancer
Siddhāṁśa, also called Chaturvimshamsha or D24, divides each 30° sidereal rāśi into twenty-four 1°15′ portions. The first portion begins from Leo in odd D1 signs and Cancer in even D1 signs. The default here counts forward through the zodiac in both cases; after twelve portions the sign sequence repeats. That is the conventional assignment documented beside the Siddhāṁśa passage in Bṛhat Parāśara Horā Śāstra 6.22–23.
A published analysis by P. V. R. Narasimha Rao argues that the same passage can instead be read as counting backward from Cancer for even signs. Choose that alternate reading in the form to compare it. The two modes agree for odd D1 signs and disagree for most even-sign portions; neither mode changes the original D1 sky positions. The calculator uses this site's independent Astronomy Engine 2.1.19 D1 positions and approximate Lahiri ayanamsha.
How to read the result
The table keeps each original D1 sidereal sign and degree, then gives the numbered D24 portion, starting sign, counting direction, and derived D24 sign and degree. The South Indian diagram fixes signs in place and marks the transformed D24 Lagna. A D24 degree expands one 1°15′ interval to a 30° coordinate; it is a mathematical transform, not another observed planetary longitude.
Use the D24 method guide to check exact boundaries and the sign-convention difference. This is a reference for a traditional learning-related varga. It cannot measure intelligence or predict a course, examination result, or academic outcome.