I have been buying alot of astronomy and telescope books of late--primarily to augment my new telescope. This is one of the better ones , since it is really much more substantive than the "cheerleading" books that are more useful at gracing the coffee table than the accessory tray of a telescope in use. The major plus feature for me is the format of the illustrations , which show the objects through a mirror type diagonal. Most , if not all , observations by amateur astronomers use this convention these days. The author goes into adequate detail on double star observing : measurement of position angle and seperationare very well explained.
I have found a few different astronomy and telescope books that are totally free. They are in a couple of different formats including the kindle format and epub. You don't have to actually have a kindle to read the kindle books though. They have a nice little free kindle program for your computer. You can get that free application right here: Most of the links below will take you directly to the amazon site where you can download the book.