[Update (May 24/14): Print-O-Matic has ceased working. It has therefore been deactivated & deleted from this site.]
Update (June 8/14): The Print-Friendly & PDF Settings plugin has been installed in Print-O-Matic’s place, and seems to be working well.
The short-code being used is:
(Where #post-13 is the DIV id corresponding to the post in question.)
See the Print-O-Matic site for further documentation regarding short-codes.