Scales may be used in Forums, Glossaries and Assignments.
Scales may be created for individual courses by Teachers with editing rights or Administrators.
Site-wide scales may be created by Administrator by "promoting" a scale created for a course, via the "Scales" link in any course Administration block.
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).