X-bar Chart Based on Six Sigma to Continual Quality Improvement: Implementation on Oil Vapor Pressure Characteristic, at Yemen’s Aden Oil Refinery. Humanities and Educational Sciences Journal, [S. l.], n. 25, p. 671–699, 2022. DOI: 10.55074/hesj.v0i25.549. Disponível em: https://hesj.org/ojs/index.php/hesj/article/view/549. Acesso em: 26 may. 2026.