I heard an interview with the author a while back on NPR. The book had some interesting bits in it. The author tried to make it exciting and put too much story into it. I enjoyed the history of the compass and how navigation changed as a result. Also cool was how that navigation was then applied to discovery. I was really impressed that the ancient Chinese who used the compass as a diving tool knew about declination. The compass had to travel to the Mediterranean though to find use for navigation.
I also found this way cool chart showing the variation of declination over time (1590-1990).