With the display rules you can visualize simple values (element properties and simple item attributes). If item attributes are calculated using an expression, the display rule no longer works.

attached is a very simple example:

Each square in the dgn has an item attached with a number attribute "Value" (1,2,3,4,5,6) and another "Value_Calc" with the expression "this.Value * 2"

The display rule works with "Value" but not with "Value_Calc"

This is intended to be used to visualize a caluclate CO2 footprint of buldings, where materials can be selected from an Excel pick list and the CO2 value is calculated based on Excel lookup values and the volume of the elements.