In this study, the 13 key steps of the SG were defined, and OCHRA was considered a valuable assessment tool for surgical performance and potential hazard zones. Most consequential errors are made during dissection of the greater curvature and during stapling of the stomach. Errors during the start of mobilization of the greater curvature and repositioning of the stapler lead to longer duration of the procedure and are associated with a higher risk of postoperative complications.