This app helps to give you two level discounts in Sales and Invoices. There will be two discount fields in sales order line and invoice line in which the first discount field is applied to the unit price, then the second discount field will apply to the discounted unit price.
In the above example, discount I and II is 8 + 2. This is not 10 but it is 8% discount then 2% discount after that. Let’s say unit price is 100, so after first discount with 8% will become 92. Then 2% discounts from the first discounted unit price of 92. Which is 1.84 here. So final unit price become 90.16 .
The same in invoices also. This two level discounts will be mapped to customer invoice when we generate invoice from sales order.
To get this feature, You have to enable in sales settings. Sale -> Settings -> Allow discounts on sale order line.