Picture all rectangles, sometimes clumped together, labelled with long strings of digits and letters, and with either solid or empty arrowheads leading in and out.
Some of the labelling indicates where in the machine the part belongs; its module, board, and location on board. Some of it tells about the function of the part, too. But that is the info I need most, and it is much less clear.
At long last I've got an example. The image is pretty big, so I've got just a piece of it here; click on it to see the whole 400K image. I believe the little snippet here represents three AND gates (one of which has only one input!) feeding into a NOR gate. The larger image is a circuit that decodes a four-bit number (in some odd encoding, of course) into seven outputs for driving a 7-segment LED. Take a look!