They ate different schematics and cutaways of various engines, gearboxes, injectors, pumps etc. An engineering minds tickle.
examples




http://www.technolab.org/content/hako/e ... d=section9
http://www.technolab.org/content/hako/e ... =section10
http://www.technolab.org/content/hako/e ... =section11
http://www.technolab.org/content/hako/e ... =section12
http://www.technolab.org/content/hako/e ... ws_cutaway
Gerrit will like this one
http://www.technolab.org/content/hako/e ... d=section4
http://www.technolab.org/content/hako/e ... d=section3
http://www.technolab.org/content/hako/e ... d=section2
http://www.technolab.org/content/hako/e ... d=section1