The Nordic softwood grading rules, also known as the "Blue Book," is a set of standards and guidelines for the grading of sawn timber produced from Nordic spruce, pine, and fir trees. The Blue Book is published by the Nordic Timber Council, which is a cooperative organization of the forest and wood industries in Denmark, Finland, Norway, and Sweden.
The Nordic softwood grading rules consist of four main parts: grading principles, visual grading rules, machine grading rules, and marking rules. These rules apply to sawn timber produced from roundwood with a minimum diameter of 10 cm, and they cover various aspects of grading, such as size, shape, strength, and appearance.
The grading principles in the Blue Book are based on the strength and stiffness properties of the timber, and they take into account the natural variations in the material. The visual grading rules provide guidelines for grading based on the visual appearance of the timber, while the machine grading rules use automated equipment to measure and grade the timber.