Quote Originally Posted by James T. Braha. Ancient Vedic Astrology for the Modern Western Astrologer
Ancient Hindu sages have given out a wealth of information concerning the conditions which strengthen or weaken the planets. An exceptionally detailed computation system has been devised to delineate these strengths. The system is called shad bala, or "six strengths." The significance of shad bala is that it reveals whether a planet will produce positive or negative effects, for power in this system enables a planet to function well and give benefits, while weakness destroys this ability. Clearly, a powerful or well-disposed malefic, such as Mars or Saturn, will give good results, while a weak or afflicted benefic causes problems and misery.

The calculations of shad bala take many hours, and although some few astrologers will take the time to do them, most do not. For there are so many basic conditions which are easily discernable that to go through the tedious process needed to ascertain the exact numerical strength of a planet seems unnecessary. This is not to say that shad bala does not produce precise, efficient, and useful information. It does. However, the procedure is simply too time-consuming. And in any case, good results are achieved if the essential elements of shad bala are used even without mathematical precision. In this book just the basics will be given. For those who wish to learn the calculations, there are two books which teach the method:Graha and Bhava Balas, by B.V. Raman, and Constellational Astrology, by Robert De Luce.

Of the 6 sources of strength, the first 3 are easily observable, while the others are more obscure and therefore generally ignored by most astrologers.