var coup1="12345-6";
var coup2="GOLD15";
var coup3="GOLD20";

function CalculateOrder(form) {

 if (form.text1.value == coup1)
 {
 form.discount_rate.value = "10";
 form.discount_rate2.value = "10";
 form.on1.value = "Coupon";
 form.os1.value = "Discount 10%";
 }
  if (form.text1.value == coup2)
 {
 form.discount_rate.value = "15";
 form.discount_rate2.value = "15";
 form.on1.value = "Coupon";
 form.os1.value = "";
 }
  if (form.text1.value == coup3)
 {
 form.discount_rate.value = "20";
 form.discount_rate2.value = "20";
 form.on1.value = "Coupon";
 form.os1.value = "";
 }
}