You can centralize the expressions used in the objects by defining variables.
To define a varaaible: In the Settings Menu> Variables overview option press Add button to declare the variable name. And use the Definition (text area) to declare the expression that the variable will represent.
In the tables - wherever you are using the expression/ formula just replace it with the variable name....try with some simpler ones to start with.
This forum already has a wealth of info on these topics.....search and you'll find.