Nondestructive evaluation procedures are now widely used in the forest products industry. These procedures rely upon nondestructive tests to evaluate important physical and mechanical properties of wood-based materials and began with fundamental research during and after World War II. An important outcome was the evolution of machinery and process for grading lumber and veneer. A dedicated group of scientists and engineers conducted and adapted this research for industrial use and developed equipment to make accurate measurements of wood properties in a production setting. One of those engineers, Dr. Friend K. Bechtel, spent over 40 years developing modern testing equipment for use by the forest products industry. Among his significant contributions to the nondestructive testing field is his fundamental analytical work. Most of his design work began with a thorough evaluation of a test method, starting with underlying physical and mechanical principles. As an industrial research engineer, he focused on designing quality equipment that would provide accurate information to manufacturers and users of wood products. This publication describes some of his work in context with that of others, some previously reviewed and published and some not. It begins with a history of the industrial development of the machine stress rating lumber grading process. It then summarizes analytical work that delves into the effects that nonhomogeneities frequently found in wood products have on their mechanical properties.