Graha and Bhava Balas by B. V. Raman
B. V. Raman's Graha and Bhava Balas is the one book that sets out shadbala in full — not as rules, but as a computation. Raman takes a single chart — a woman born on 16 October 1918 at 14:06:16 local time, latitude 13° N — and carries it through all six sources of strength, down to every sub-component and to the total in rupas.
Its value for verification is hard to overstate. Every astrological program computes shadbala its own way, and they can differ by half; but Raman's figures were obtained by hand from tables of 1940, and one can check against them. We did: our chesta bala — the hardest of the six — agreed with his hand computation to between one hundredth and one tenth of a shashtiamsa for all five planets for which it is computed at all.
The book also explains why programs disagree. Raman measures dig bala from the true meridian, whereas many programs take an equal-house point from the ascendant — and on the four "meridian" planets that yields a difference of exactly 2.7 shashtiamsas. He gives nathonnatha bala in two presentations, "methods A and B", noting that the principle is the same in both: five virupas per hour from midnight, with midday taken as apparent noon and the birth time converted to local apparent time by the equation of time. Chesta bala he computes from his own mean-motion tables with an epoch at Ujjain midnight.
The chapter on drik bala deserves separate mention for its broken aspect curve: the value rises from zero at 30°, reaches 45 at 90°, falls to zero at 150°, and jumps to 60 at opposition. Nowhere else is that curve stated in quite this form, and it is precisely what distinguishes the Parasari school from the rest.
P. V. R. Narasimha Rao — author of the Jagannatha Hora program — refers his readers to this book in Vedic Astrology: An Integrated Approach: he gives no shadbala computation at all, directing the reader to Parasara and to Raman, and remarking that "there are minor differences between the definitions used by" the various programs. So this is a primary source in the strict sense — the one the modern computing tradition itself points to.
Thirteenth edition, 1992, 129 pages. The recognised text is marked page by page in the form ===== стр N =====, which makes it easy to search and to cite with a page number.