Mechanical watches are relatively complicated, and it takes two or three years to learn them accurately. The types and styles of watches are different, and the structures of watches produced in different countries are also different. It is very difficult to really know how to disassemble and assemble so many kinds of watches. There are one or two hundred parts in another watch, and each part may break down. You need to learn fault diagnosis, which requires you to have rich experience and superb technology, and you need to constantly explore and improve in long-term maintenance practice.