Phan Khánh Linh, and Nguyễn Thị Anh Vân. “Applying Six Sigma Method to Improve Product Quality of Automatic Water Valves: Online First: 30/06/2026”. Journal of Technical Education Science (June 30, 2026). Accessed July 7, 2026. https://www.jte.edu.vn/index.php/jte/article/view/2125.