Create a new purchase order and add discounts in any of the three
discount fields given. They go in order of precedence so discount 2 will
be calculated over discount 1 and discount 3 over the result of discount
2. For example, let's divide by two on every discount:

Unit price: 600.00 -\>

> - Disc. 1 = 50% -\> Amount = 300.00
> - Disc. 2 = 50% -\> Amount = 150.00
> - Disc. 3 = 50% -\> Amount = 75.00

You can also use negative values to charge instead of discount:

Unit price: 600.00 -\>

> - Disc. 1 = 50% -\> Amount = 300.00
> - Disc. 2 = -5% -\> Amount = 315.00

- When the purchase order is validated, the discounts will be added to
  the corresponding vendor pricelist.
- Vendor pricelists can be edited as well with their corresponding new
  second and third discounts.
- A default second or third discount can be set in every vendor *Sale &
  Purchases* tab.
