At the moment we do not support automatic grade calculation. As I'm sure you can imagine, one of our biggest marketing challenges is convincing teachers that this is not an auto-grader. So many teachers assume that any technology around essay grading is going to try to do the evaluations for them. So we've shied away from any feature that takes any evaluative power out of the teacher's hands.
It also turns out that it's a bit complicated to support all the different ways a teacher might want the rubric tallied up. One simple example: is each piece of evidence worth X points? Is there a max (e.g. 3X points for 3 pieces of evidence)? Or do we just average all the evidence evaluations into a single score to generate points?
Eventually we probably will introduce auto-tallying. But the score that it produces would just be a suggestion and could still be overridden by the teacher.