Calculation with formula in Product Template is not correct whe using %

Calculation with formula in Product Template is not correct whe using %

Hi all,
I new to Zoho an using it as a try-out.

I would like to calculate the Purchase Price based on Unit Price & vendor discount.
So:
I add 2 fields on the template
Vendor Discount as %
Purchase price a formula field (Integer) with the following formula
Unit price - ( Unit price * Vendor discount)

This results in a negative number, the calculation does not take into account that Vendor Discount is a %.

Next Q. how can I update the whole product list when I changed the formula .