The 100-ml (3.4-ounce) maximum for carry-on liquids began in 2006 as a blunt response to a foiled transatlantic liquid explosives plot. At that time, checkpoint scanners were effectively digital shadow puppets. They produced 2D images in which a bottle of shampoo and a dangerous substance could be hard to tell apart, especially when such an object was buried under a tangle of charging cables and power bricks. The solution was a work-around: shrink the liquids to 100 ml until the machines could cope.