Custom field for inventory and sales invoices that works with other fields

Hi, I am new user of Manager and I found it very easy and comfortable to use. But I have some difficulties as I want to add “discount” and “Trade offer” fields in inventory items, with the help of Manager guide I managed to add fields but it does not affect the average cost of the product. I also want to add “bonus” field in sales invoice that should be calculated with Total Amount.

Average cost only changes when you purchase additional inventory via purchase invoices. The calculation is based on what you’ve actually paid over time.

As for active calculations in custom fields, Manager won’t do that at present.