For the same reasons that the gradedisplaytype setting was removed from gradebook user preferences, and added to the grade_item table, it would appear that the decimal points should also receive the same treatment.
1. "Real" and "Percentage" display types both use decimal points
2. It makes no sense giving each grade_item control over the gradedisplaytype without also giving control over how these 2 types of display are... displayed
Additionally, constants do not need to be defined for the decimal points, because it would mean defining 12 new constants (0-5 for real and percentage display types). Simple integers will suffice.
It is thus proposed to add a "decimals" field to grade_item (tinyint(1)) and apply the same type of class and form changes that were applied to the gradedisplaytype setting.