This part of ISO 8791 specifies a method for the determination of the roughness of paper and board using the Sheffield apparatus. The method is applicable to papers and boards which have Sheffield roughness values between 10 and about 3 000 ml/min. It is not suitable for soft papers which allow the lands of the test head to indent the surface, or for high air-permeance papers which allow a significant flow of air through the sheet, or for papers which will not lie flat during the test