Custom Field Discount Calculations

A field has been added in the sales invoice screen. I want this field to be adjusted to collect the discount value of each item and the value of the total item on the invoice so that I know the total amount of the discount on the invoice

Are you trying to apply different discount rates for different line items in item table and then at the bottom wants to show a summary of Discount received at each particular rate of Discount?

Becuase what I see now on your screenshots (+1 I replicated), the additional discount is applied on the basis of selection made, either to be on Grand Total or Net Total.

Yes, I want to see the value of the discount on each item
There are 3 elements in different proportions
1- Quantity 10 * Price 500 Discount Rate 20% Discount value equal to 1000
2- Quantity 5 * Price 100% discount rate 30% discount value equal to 150
3 - Quantity 4 * Price 300 Discount Rate 22% Value of the discount equal to 264

In the case of a discount on the total number of lines 10%
The discount value is 528.6

The total amount of the discount on the invoice

I don’t think line item wise different discount rate is possible in v10. But i believe it is important feature to be added in the upcoming versions.

It is really important to add it in future versions
Is there a script that currently does this on version 7