The price of a combo item can be set as a fixed amount or as a percentage of the price of the menu item associated with it.

The price of a combo item as a percentage of the price of the menu item associated with it

In the "Price Types" directory, on the Properties page, check the box next to the "Percent in Combo" property. 

If the "Percent in Combo" flag is set, then the "Default Combo Item" property appears. This is the percentage that will be set for all combo items automatically. 

On the "Combo Items" page, in the "Basic" properties group, two properties will appear: "Clear Price" and "Discounts (Markups)". 

In the "Combo Groups" directory, in the "Prices" property group, the price will be displayed with a percentage sign "%". The price of the combo item in this case is calculated as a percentage of the price of the menu item associated with it.

Combo item price as a fixed amount

In the "Price Types" directory, on the "Properties" page, the flag opposite the "Percent in Combo" property is not set. 

The "Combo Items" page shows how the price of a combo item is formed. When editing manually, the price of each item is set manually. 

In the "Combo Groups" directory, the price of the combo item is added manually as a fixed amount.