Flow restrictor used to calibrate air-leak instruments
There are numerous published inter-conversions of data between various roughness/smoothness testers. These should be used with the understanding that the only way to achieve unequivocally valid data of a particular instrument type is to use the specified instrument for the required testing. There are strong proponents for each of the instruments discussed here, as well as additional instruments familiar in different parts of the world. The user must make the decision which instrument is most useful for a specific property measurement task.
The following chart shows some smoothness values for different papers measured with the Sheffield, Gurley and Bekk testers.
Source: Abbott, J.C., "A Training Presentation Prepared for Technidyne Corporation", April 4 & 5, 2000.