Weather forecast -7 ~-1 What do you mean?

Well, the front is the lowest (below zero) or the highest (above zero). For example, -7 ~-1 (the previous number represents the lowest temperature below zero); If 7 ~ 1 (the previous figure is also the highest temperature). The sentence accentuates that meaning. What is the lowest or highest temperature? Let's see clearly that this is also a special sentence-making method.