difference between symptom and root cause

The SIMPLE version they want: a SYMPTOM is what you can see going wrong; the ROOT CAUSE is the underlying reason it happens. Fixing the symptom makes the problem go away temporarily; fixing the root cause stops it from recurring. A classic example: 'the film is non-uniform' is a symptom; the root cause could be a temperature drift, a worn target, or a chamber-condition change. The key line: 'Fixing symptoms is like treating the fever and sending the patient home — the infection comes back. Root cause is why the fever happened in the first place.' WHY IT MATTERS FOR GPS: field pressure tempts you to patch symptoms; the GPS standard (and CAPA, Lesson 4) is root cause + verify it holds. Show you'll resist the easy patch.