Because this item simultaneously cut two lines when line any one the end of roll. Operator will stop cutting machine to join the film. The films must be inserted through roller bag (as picture), which will have to press the switch to only feed roller bag work. (Sealing knife and perforating knife is not working), the roller will pull film the two line, both line that was joined and not join so that the film was joined complete. Operator will press the switch for work of cutting machine, film two lines is sealed wrong position. Operators have to separate good film and no good both two lines. But in this case the operator culling of no good only one line on the reel. So there goods are not seal leak to customer.