Hi,
My colleague will send you the documentation in German by e-mail.
Do you mean the discount when you're entering a custom Calculation Rules (like "Price modified after tax per bill")? In this case it is possible for us to implement an option to enter the value as percentage for you as a paid service. Our estimation is that 4 hours of our support time would be needed to implement this feature. For pricing, please see:
www.artio.net/de/e-shop/support-services/joomla-support-1h
Thank you for reporting a display problem. We'll fix it in next version.