This is the only book on sundials that I am aware of that was truly written by and for amateurs. The author describes a number of different dials, as well as methods of designing and constructing them. So far, this is much like any other book on sundials I had seen. He then goes on to describe certain modifications and experiments he conducted, and some additional dials he designed, (and how they were designed.) He juxtaposes the (in hindsight obvious,) facts of the relationship between knowing the time and knowing your position, (this of course was a major driver behind the invention of the portable timepiece.)