I was trying to follow this guide: https://maestrano.atlassian.net/wiki/plugins/servlet/mobile?contentId=26706066#content/view/26706066
But when I enter negative values in virtual product quantity, the record disappears (it is not accepted).
What I want to do is make product out of raw material.
My process is : buy raw material (+), make final product out of raw material (- raw material), sell product (- final product - raw material).
If there is better way to do this, please state it too. All help is appreciated.