Mechanically graded lumber is lumber that has been tested and evaluated by a machine rather than by visual inspection. While most lumber is visually inspected and graded, machine grading is a more efficient volume service and creates cost-competitive products, while differentiating the higher strength lumber materials. It is commonly used to deliver materials for more demanding applications. Two types of machines are used to grade lumber, machine-stress rated (MSR) lumber and machine evaluated lumber (MEL) machines.