Trading spread-unilaterally add or subtract 0.5 yuan on the basis of the middle price.

For example, the median price 100 yuan/gram and the bilateral price difference 100 point (i.e. 1 yuan).

Then: the buying price is 99.50 yuan/gram, and the selling price is 100.50 yuan/gram.

When carrying out preferential activities, the bilateral price difference is 80 points (namely 0.80 yuan).