The Janka hardness test measures the resistance of a sample of wood to denting and wear. It measures the force required to embed an 11.28mm (.444 in) steel ball into wood to half the ball's diameter. This method leaves an indentation.
Wikipedia contributors. "Janka hardness test." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 11 Aug. 2015. Web. 12 Aug. 2015.