"Perfecting" is done by the use of a special cylinder. In normal operation the printed sheet from the first unit is transferred to the second via a transfer cylinder. This is done by taking the sheet via "grippers" and passing it to the next cylinder by gripping the lead edge of the sheet and then transferring again by the lead edge of the sheet. To "perfect" or print the back side the timing is changed on the transfer cylinder so that in the transfer process the sheet is picked up by the grippers of the No. 2 cylinder at the tail edge of the sheet thus effectively "turning" it over.