Appearance Inspection Methods

The method of visual inspection is based on the fact that the object is

1) Whether it is stable or not

2) Simple or not

It is easy to understand if you think in terms of
If it is stable, it can be tested by "whether it is the same as the others".

If it is simple, it can be inspected based on whether or not it is the same as it should be, which can be inferred from its appearance.