The exact meaning of gross margin?

The gross margin is not comparable between the 1 dollar and the 100 dollar stuff. If it is the same type of product, the quality difference is not big, usually the 1 dollar thing sells more, the profit is higher than the 100. When the two products are similarly priced, a 100 sells for 150 with a gross margin of 33%, and a 90 sells for 130 with a gross margin of 30.8%, in which case it is possible that the 130 sells for more and has a higher profit.