Forest Products Laboratory (FPL) of the U.S. Department of Agriculture (USDA), Wood Handbook—Wood as an Engineering Material (頁面存檔備份,存於互聯網檔案館), General Technical Report series, № FPL‑GTR‑190, Centennial ed. (Madison, Wis.: USDA Forest Service, FPL, 2010‑04), p. 2‑2.