This study was one of the first "time-motion" studies of physicians, and pioneered the application of human factors engineering and industrial principles to medical practice. The authors shadowed surgeons, who are described as "the most interesting of all mechanics," at hospitals in the United States, Canada, and Germany. Based on their observations, the authors identified the components of the work day as "necessary work," "unnecessary work," "avoidable delay," and "unavoidable delay." In order to maximize the efficiency of a typical surgical practice, they argue for standardization of surgical equipment and the hospital environment, recommend scheduled rest periods to avoid fatigue, and advocate for using technology to avoid fatigue arising from necessary work.