1981年为大气能见度变化的转折期，在此期间11个城市的能见度迅速降低、“非常好”能见度出现频率很快下降。
The turning period of visibility change took place during 1979-1981, and both the visibility and "very good visibility" frequency of the 11 cities decreased rapidly at that time.
生产率高，质量好，无渣，明弧，能见度高；
Work in high efficiency with good welding quality. No slag, opened arc and high visibility;
应用推荐