In the Assessments & Grading module > Grade Setup > Grading Scales, you can identify the grading scale that you want to use for the Overall Score.

The system will use the common grading scale configured in the "Overall Score Grading Scale" to display the overall score for all the subjects.

Now, if you want to use a different grading scale for certain subjects, just click on the setting - "Manage Weights and Overall Score Grading Scales & Passing Score Limit"

Once you click on that link, you will be taken to a page where you can set a custom grading scale for the overall score of each subject. Here you can set the grading scale for each subject as you like.

Note that if you didn't set a custom setting for the overall score, then it will just follow the default settings that were set from the main Grade Setup page.