R. Díez, M. Conde, J. I. Fernández-Golfín, and S. Rosskopf, “Visual strength grading of structural timber of Laricio pine (Pinus nigra Arn.): comparison of results according to UNE 56.544 and DIN 4074 standards”, For. syst., vol. 9, no. 2, pp. 375-380, Dec. 2000.