Boeing became the first commercial airframe manufacturer to use the moving line concept to build jetliners when first the 717, and then the 737, production lines were transformed into a moving line. The moving line helps reduce the time to assemble the airplane and also cuts inventory and production costs. 737s on the line move continuously at a rate of 2 inches (5 centimeters) per minute; the line stops only for employee breaks, critical production issues or between shifts. Timelines painted on the floor help workers gauge the progress of manufacturing.