The National Lumber Grades Authority (NLGA) monitors structural lumber design values for the three major commercial Canadian species groupings, Spruce-Pine-Fir (S-P-F), Douglas Fir-Larch (D.Fir-L), and Hem-Fir.  Monitoring involves the collection of samples from across Canada and testing them to ensure there has not been a statistically significant change in the design values assigned to the species and grade.