Hi there, @CharlesRobin ...
Yes, the "Additional Comments" text box and under each quiz question and the "Add a Comment" text box that appears at the right side of the SpeedGrader are both different. As you might have guessed, the "Additional Comments" text box under each question is to add specific comments for a particular question you want to provide feedback on for a given student. However, the "Add a Comment" box on the right side of the SpeedGrader is more for overall comments on the quiz that you are grading for the student. From a student perspective, he/she can go to the "Grades" page, find and click on the name of the quiz, and he/she should (hopefully) be able to cycle through the quiz questions and see both the individual question feedback as well as the overall feedback. This, over course, also assumes that you have configured the quiz to allow your students to see feedback or not...which is all set up via the "Edit" screen of your quiz.
Hopefully this helps to clear things up. Thanks!
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