Letter grades limit

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Letter grades limit


At our university our academics often use a 20-point scale for grading, where 1 is the highest grade and 20 is the lowest. It is a conversion from a percentage - however it is not linear in nature and there is no calculation, e.g.

Grade 1 = 79%+
Grade 2 = 76-78%
Grade 3 = 73-75%

In theory the perfect way to do this would be to use a Letter Grade - however when we tried this we found that this option is limited to 14 points whereas we need 20. We could use a Scale instead but this would involve the academics doing the conversion themselves. Does anyone have any ideas for a way around this?