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Description
Discussion about this/related to this at http://moodle.org/mod/forum/discuss.php?d=120541.
Could we have a 'scale' in Moodle that isn't really a defined scale, but rather one that maps to the letters and percentage ranges that are defined in the letter settings in the gradebook? In other words, if letters are enabled and defined, either site-wide or on the course, teachers would have an option of 'Scale: Grade Letter' in the Grade dropdown of any graded activity. This wouldn't be defined in mdl_scale, but rather from mdl_grade_letters. Moodle would simply know that this particular scale gets its values from the grade letter values, and would allow teachers to select the letter as the grade for an activity, rather than using a number that Moodle would then display as a letter.
Gliffy Diagrams
Issue Links
- has a non-specific relationship to
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MDL-17258
Use "Letter" grades in gradebook, assigns desired numeric grades for you
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- Open
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- has been marked as being related by
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MDL-21631
Add more preinstalled scales
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- Open
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MDL-46180
Scales and letter grade changes coming out of the Gradebook Workshop
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- Open
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- is duplicated by
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MDL-17258
Use "Letter" grades in gradebook, assigns desired numeric grades for you
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- Open
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Activity
Oh, scales havn't manual percentage for they items, but letters have it 
See patch available on MDL-17484. And discussion at http://moodle.org/mod/forum/discuss.php?d=140907.
Having extensively studied the question, it is virtually impossible to automatically derive a value to a letter based on the existing letters intervals.
By cons, if Moodle had initially a valid scale using letters, we could deduce and generate an interval values converting to letters based on this letter scale.
As this is not the case, I think the solution would be possible to associate a custom value to a specific element of a scale. View tasks:
https://tracker.moodle.org/browse/MDL-44673
https://tracker.moodle.org/browse/MDL-18881
I also think this is what is planned:
http://docs.moodle.org/dev/Scales#Proposed_Database_Structure
Please check out LSU's better letter grades.
Here is the patch against 2.7.
https://github.com/lsuits/gradebook_patches/blob/master/better_letters.patch
This solves the letter grade issue and provides a basic framework for a reimagining of scales as discussed in the gradebook working group.
This will be fixed soon in the duplicate issue MDL-17258
How about to generate just one another scale by submiting changes into the letters?
And use it by default...