The reasoning
Systematic read: gas pattern (bowel calibre and distribution) → extraluminal gas (free, wall, biliary, portal) → soft tissues (organ outlines, psoas, masses) → calcification (urinary, biliary, pancreatic, vascular, phleboliths, appendicolith) → bones → lines and foreign bodies. The supine AXR is standard; erect/decubitus films show fluid levels.