Blackboard Grade Calculator

SUMMARY:
Tallies grades in "Comments & Markups" section that has the format: "x/y [ grader explanation text here or empty ]" (e.g: "1/10 -9 No work shown", where x=1 and y=10 for this specific grading.)
Displays the tallied grades by modifying the "Comments & Markups" header as "Comments & Markups [sum(x)/sum(y)]"

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BE CAREFUL!
Best practice is to define the score ratio at beginning of a comment.
For annotations that do not contain a grading, but a ratio as an explanation to a question must be observed carefully, since they would be calculated as well.
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USAGE:
Simply download and install the extension to automatically view the sum ratio in the header.
Click on "Comments & Markups [sum(x)/sum(y)]" header or the "A+" icon on top-right of the chrome screen (as shown in the first screenshot) to view grader distribution (as shown in the second screenshot.)

CREDITS:
Thanks to Qiuyin Ren and Syed Hossain for the idea.