When you add a new Gradebook, the calculated percent will show negative at first (as in the screenshot below).
In order to get it to show the proper rubric calculations, we need to make a few changes.
Mouse over Grade Book and then click on Grade Book Setup.
Then click on Class Settings and from this page click the edit button.
Once you click edit, you will see additional drop-down menus. You need to change Grading Periods to "Grade Score" and once done hit Save.
After this your percents should be calculating properly as in the screenshot below.