The final calculated grade is the grade that is calculated by D2L based strictly on the scores that students received on the various grade items in the grade book. It can not be edited.
The adjusted final grade is the grade that may have been adjusted by the instructor. For example if a student received an 89.95% as a final calculated grade, in the adjusted final grade an instructor could edit the students final grade (usually giving the student a few extra points) so the final adjusted grade is 90%. The student would receive an A instead of a B in the course.