In order to investigate stiffness and strength properties of sawn timber, it is common practice to load the specimens and measure the deflection. The results obtained from measurements are strongly influenced by grain deviation with respect to the longitudinal direction and by variation of material properties with position in the log. Effects of this type are often explained by the presence of juvenile wood and compression wood. In addition to being influenced by fibre misalignment and variation in properties, the grading procedure is often disturbed by twist deformations of the board caused by spiral grain.