The Exakta Cameras Guide is a must and unfortunately really the only such book on these cameras. Sadly it is lacking in history of the cameras and company but it also explains that information is very hard to obtain given World War II, the destruction of the factories, The Soviet Occupation and other factors leading to loss of physical records, photos, etc. The book is however filled with crisp B&W images of each variety of Exakt and a detailed description and Serial #'s to help identify the often similar looking models.
If you are a collector or user of vintage Exaktas this book is a must! Buy with confidence but look for a bargain used copy as the new ones are pricey!