Red pen: 1. Long-term medical advice, such as changing majors after surgery, needs to be crossed. 2. Surgery, surgical site identification: surgical site, skin test, identification of some tests (tuberculin test), 3. Auxiliary inspection abnormality identification table, 4. Identification of allergic history, 5. Signature of superior doctor. Blue and black pen: document signature, doctor's advice signature, header auxiliary inspection. Now most of them have been replaced by electronic signatures. Black is never used. I think the nurse used it.