Abstract: Metal strip stock in a rolling mill, paper or the like is constantly monitored for flatness across its width during processing. Monitoring probes carried by a common header or manifold emit air streams which impinge on the moving strip to produce a back pressure on which the nozzle-like probes float and seek to maintain an accurately predetermined fixed air gap between the tips of the probes and the strip or web. Flatness irregularities, whether depressions or humps, in the strip are reflected by movements of a probe or probes, an such probe movement causes a change in the outputs of associated linear voltage transistors which are linked through a signal modulator means to a visual display of strip flatness irregularities. The system is sensitive and accurate as well as automatic once installed and set into operation. Physical contact between parts of the system and the product is avoided.