A printing unit comprises a pair of blanket cylinders that form a nip through which a substrate can pass as ink images are transferred from the blanket cylinders to both sides of the substrate. The system and method automatically check security to protect a PC from computer hacking, viruses, worms, Trojan horses, etc. The mounting apparatus includes the seat mounting means, the cover mounting means, post holders which overlie the bowl flange apertures, and connecting means joining said seat and cover mounting means and the post holders to permit rotation of the seat ring and cover between a generally horizontal use position and an over center storage position.