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2. ASTM D1990-16 (2016) Standard practice for establishing allowable properties for visually-graded dimension from in-grade tests of full-size specimens. ASTM International, West Conshohocken
3. ASTM D245-11 (2011) Standard practice for establishing structural grades and related allowable properties for visually-graded dimension. ASTM International, West Conshohocken
4. ASTM D4761-13 (2013) Standard test methods for mechanical properties of lumber and wood-base structural material. ASTM International, West Conshohocken
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https://CRAN.R-project.org/package=gridExtra
. Accessed 1 Nov 2018