This part of ISO 8791 specifies a method for the determination of the roughness of paper and board using the Bendtsen apparatus. This part of ISO 8791 is applicable to paper and board which have Bendtsen roughness values between about 5 ml/min and 3 000 ml/min when measured with variable-area type testers and between about 50 ml/min and 5 000 ml/min when measured with electronic type testers. It is not suitable for soft papers which allow the land to make a significant impression on the surface or for high-air-permeance papers which allow a significant flow of air to pass through the sheet, or for papers which will not lie flat under the measuring head.