《元史·列传·卷七十一》
于是按照旧制设盐亭灶户，三年比一次，排定名次，这是世祖时的旧制。
乃如前除盐亭灶户，三年一比附推排，世祖旧制也。
So according to the old system, the salt Pavilion stove household was set up. It was compared once every three years to determine the ranking. This was the old system of the Shizu.