This volume is an appendix to Volume 1 (Northern Hemisphere to -6) and Volume 2 (Southern Hemisphere to +6). It's basically a huge printout of summary data for each and every deep sky object mapped in the previous two volumes. Size, shape, magnitude, separation (for doubles), etc. Basically everything you need to determine if an object is a feasible target and to confirm your sighting once you've found it. This book is big and heavy, so don't plan on field use unless you have a portable desk or table to work from.