Gives basic requirements for apparatus and general operating procedures for determining the air permeance of paper and board in the medium air permeance range. Suitable for papers and boards having air permeances between 1 x 10 to the power -2 and 1 x 10 to the power 2 micron m/(Pa.s), but not for rough surfaced papers and boards, such as creped and corrugated papers, which cannot be securely clamped to avoid leakage. Includes apparatus, sampling, conditioning, preparation of test pieces and test reports.