End users are assured the boards will meet the specifications associated with the grade stamp. MSR offers superior lumber with less variability in stiffness, allowing for designs that hold to tighter tolerances and guard against expensive failures. Visually inspecting lumber, on the other hand, is subject to human fallibility and a 5 percent off-grade tolerance is built into the grading rules to allow for this. Boards pass by at 50 to 60 lugs per minute, leaving graders with less than three seconds to evaluate a board. Many visual characteristics don't correspond with mechanical properties.
Mechanical properties are what make structural products perform.
If a piece of lumber fails during or after construction, a suitable repair can be a labor-intensive hassle that wastes wood. The cost of repairing critical components in houses and light commercial construction can be considerable. Truss builders, for example, face repair costs at least ten times higher than if the truss was built with superior wood from the start. An alternative to using MSR lumber is to over-design products in order to provide a margin against possible defects and the associated repair costs. However, in the long term this can be far more expensive and still not as reliable as simply purchasing accurately-graded MSR lumber.