Scales may be used in Forums, Glossaries (for rating) and Assignments (for grading).
The interface for creating scales is accessed by clicking the "Scales" link in any course Administration block.
Scales may be created for individual courses by Teachers with editing rights or Administrators.
Administrators may create site-wide scales by "promoting" a scale created for a course.
To achieve this, add a new scale, then use the move down arrow to move the scale from custom scales to standard scales (i.e. site-wide).