How can I change the formula for Amount on the invoices?
We have some items where the user pays the amount on three parameters - duration, quantity and rate. I used the "Custom Fields" in Items list to add "duration" column. I have also added the custom field to the invoice template. Now, whenever I use the new template now, the amount is only calculated using the rate and quantity (default fields of QB). How can we add "duration" as a multiplier on the amount?
