Great as a "let me look this up" book.
Read as an e-book. Hence the quality of the pictures were not great. However if you really want to know what makes a mechanical watch tick (...yeah I went there) I can recommend this. I read it because at some point in the future I want to design and assemble a watch for myself. This book will be helpful but it also goes on into mechanical details which, while necessary, were not very enjoyable to read.