求如下信用证条款是什么意思signed commercial invoice in 3 copies,certifyin

求如下信用证条款是什么意思
signed commercial invoice in 3 copies,certifying theat the goods shipped and invoiced conform to those described in the proforma invoice po no 7003098 no QB07CI 005 DD 14 2007 indicating
1) net and gross weight of goods.
2)the nature percentage and amount of any discount granted.
3) the unit price and total amount corresponding to each item invoiced
4) the agent's name and commission,if any
其他的我都懂
但是不知道在发票应该怎样写 we certify that.
我们的产品是阀门,那个nature percentage要怎样体现在发票中