Converting or bag making is the process of turning the roll of plastic, printed or plain, into a bag. The equipment used is capable of very exact repeat lengths. You often will see a mark on the edge of the printed bag which is sometimes called the bug mark. This mark is detected by an electric eye which causes the machine to cycle so the bag may be made. Most plastic bags are side-welded by applying a hot knife to the plastic. It then melts, separates and seals both the front of one and the back of the next bag. This knife varies in temperature depending on the thickness of the plastic bag.