The first, second and third buy and sell points can all be classified as the first type of buy and sell points, but at different levels. So why not just say the first type of buy and sell points, because this will involve different levels, which is equivalent to looking at it with microscopes of different levels at the same time, which is too confusing for novice operators and even more confusing in actual use. The meanings of buy and sell points at different levels are different, so they should be operated at the same level, which is why there are three types of buy and sell points.