It's a very nice and useful quick reference for basic use of Nikon D90 DSLR Camera. Its size allows carry in any backpack. If you are a new owner of a Nikon D90 it is a very good reference, although the camera comes with a Quick Guide that is deeper than this. If you've already been using a Nikon D90 for a while (possibly another Nikon DSLR too) does not need this quick guide because you know what's there.