A method for measuring and displaying the flatness of a rolled steel sheet is disclosed that includes the steps of measuring tension in the sheet at a plurality of locations on the surface of the sheet and determining a plurality of tension ranges into which the sensed tension level can fall. A color is associated with each of the tension ranges, and a representation of the sheet is produced that is made up of a plurality of regions, each region having a color corresponding to tension range into which the tension sensed at the corresponding location on the surface of the sheet falls. A device for carrying out this method is also disclosed.