If a value is not listed in the property page, its initial value will be zero or an empty string "". Therefore you do not need to list an alterable value or string if you want it to start at zero.

Click on this button to add a value to the list. Then you simply click on the number or string and change it : the value indicated will be used to initialise the alterable value at runtime. You can also rename the value or string by double clicking on the name, or right-click the name and select the Rename or Delete command in the popup menu. Note: you can delete only the last value.