Step 1 - Go to the gradebook

In the class you want to use mark codes for, click Gradebook setup in the Class Administration block to open the gradebook setup page.

Step 2 - Create a new grade item

This will contain the list of possible mark codes, and you will set it to be the mark code you want.

Just click Add Grade Item at the bottom of the screen.

Step 3 - Name the grade item

This is what the marks returner will see, so name the grade item Mark Codes.

Step 4 - Select scale as the grade type

Drop down the menu and select Scale.

Step 5 - Select the scale and hide the grade item

Step 7 - Save and return

You can now choose the category the mark code grade item will appear in. If you have it, the Administrative category is a suitable place. Then click Save changes and you will be returned to the gradebook setup screen.