A procedure for evaluating a specific property of paper that is officially authorized by the Technical Association of the Pulp and Paper Industry. There is at least one Official Test Method for each of the vast multitude of paper properties. A TAPPI Official Test Method must provide accurate and reproducible results among different paper testing laboratories over a period of time. Test methods also describe the calibration of testing equipment, the procuring of representative paper samples, and the creation of a carefully controlled environment. The addition, revision, and excision of Official Test Methods by paper professionals and laboratories around the world is constant. Procedures that are not sanctioned as official by TAPPI but which are useful in practical application are called TAPPI Useful Test Methods.