Measuring the flatness of a cold-rolled steel strip or aluminum foil is a vital aspect of production quality control. Cold lamination control based on the results of this measurement crucially affects production efficiency, but further processes can modify flatness, which can be lost when the strip becomes cold. We describe a low-cost flatness measurement system to monitor this property at several production line points. The system is composed of a capacitive sensor array, some microcontrollers, and a PC for computing and visualization. Measurements on a production line are provided and analyzed.