Containerization has lowered shipping expense and decreased shipping time, and this has in turn helped the growth of international trade. Cargo that once arrived in cartons, crates, bales, barrels or bags now comes in factory sealed containers, with no indication to the human eye of their contents, except for a product code that machines can scan and computers trace. This system of tracking has been so exact that a two-week voyage can be timed for arrival with an accuracy of under fifteen minutes.