哪位大侠帮看看，这段话倒底是什么意思，多谢！
FOB Rotterdam discount Gross-18$ netto -13$ annual and 500 000mt SPOT
Rotterdam, SPOT Houston SPOT Dubai, each named port at a discount 26 USD /
t of the total average cost per metric ton for each of three consecutive
business days preceding the date of signing the contract, based on average
cost, published European Marketscan "PLATT", divided by three.