I got this book to go along with a Tibetan Astrology computer program sold by Matrix Astrology Software. The software doesn't have a manual but from what I can tell produces accurate computations. The book has some bugs in computation. Put the two of them together for the best of both worlds
As the only source for Tibetan Astrology so far in print, this book is a must have. It almost makes sense out of a system that even the Tibetans find confusing!
There is also a lot of very good material on Tibetan Buddhism included; material that you don't often see.
However, beware Table 22 (the main table you use to convert Western Dates to Tibetan Dates---the very first step in working with Tibetan Astrology for westerners). It is *riddled* with errors.
That said, there is information here that you'll find nowhere else. Definately a "must have".