Ah, if you want the calculation to take place when the check-box is ticked, use this:
if(this.getField(cbNonDiscount).value != "Off") {
Instead of this:
if(this.getField(cbNonDiscount).value == "Off") {
Ah, if you want the calculation to take place when the check-box is ticked, use this:
if(this.getField(cbNonDiscount).value != "Off") {
Instead of this:
if(this.getField(cbNonDiscount).value == "Off") {