How can I set the percentage of the meal cost within the room rate?

How can I adjust my meals so that they account for a certain portion of my room rate?
My breakfast is included in the room rate and accounts for 20% of the room price. How do I set this up?
This function is only available if the option „adavanced“ has been selected for functions under Settings/User interface.

Go to Settings/Price List and change the setting under 'Price Adjustment' to 'Automatic/Percentage'.
Then, under 'Percentage', enter the correct percentage of the meal cost.
Save your entries using the Save button or the disk icon in the taskbar.