As a long-time believer in biorhythm (since 1970) I was looking for an updated book since the last one, "Biorhythm-A Personal Science" did not have any subsequent years after the late 90's. This book is good for beginners, but I was annoyed that all I could get were the numbers. There was no mention of what to do with the biographs once I got the numbers. The old books had a special ruler to draw the lines with, and the previously mentioned book worked everything out for you. Best bet? Buy the software instead.