You can choose the type of grade scale by selecting “Grade Scale” from the settings menu within the Grades tab.
The blue box on the bottom of the window will update based on your chosen setting.
The grade scale will either be percentage or GPA based as indicated in the Grade Calculation settings.
The far right column in the grade scale settings will indicate the percentage/GPA that will be calculated when a letter grade is submitted. This can be modified for the overall course. If you wish to change the value on an assignment or individual student level, you will need to enable the letter grade override option within Grade Display.