Here is a very interesting book that explains where do the numbers and why, all with a style and vocabulary accessible to all, even a little playful side (there is sometimes question of zombies ...). By cons, we must anyway be a little maths to enjoy some demonstrations. For my part, I was a little frustrated and I wish that solving some equations are a little more detailed and explained. It is true that this was not the purpose of this book but it would have allowed me to enjoy it more fully.