Harmonic Charts is an excellent text for exploring harmonics, an aspect of astrology that is not used as much as other more mainstraem approaches to the birth chart, but is, in my opinion, a very fascinating branch of study in the filed.
Hamblin's book is very accessible, unlike other books on this topic that i have read, that seem to muddy the waters rather than clarify them. If you want to learn this technique and understand it, without loosing in depth, this book is a very good place to start. I really liked it. Lots of case studies to play with, lots of interesting observations on the mathematical nature of the chart, on aspects and even on the application of harmonics to synastry.
As a former physicist and mathematician, I love harmonics as this branch of astrology feels very pure and very close to the essence of things...are numeric patterns the underlying language of life? Play with Hamblin's harmonics and find out for yourself ....Excellent mind fun.