Currently it is possible to select both a unit and a value mapping for an item. Then the value mapping will be applied to the formatted item value with units. For instance, if the value of an item is 1024 with units B, it will be converted to 1 KB, and we can create a value mapping "1 KB" -> "Some string". This seems unnecessary and counter-intuitive. We should isolate these two features and removed the ability to create items with both units and value mappings.