Define the variables to be used:
In formulas.
As scheduled units in work breakdown structures.
You can define variables that differ from the units. But you can also link a variable to a unit.
Steps
Go to Project management and accounting > Setup > Advanced project management > Calculation variables.
Click New.
In the Variable field, type a value.
In the Description field, type a value.
Notes
All variables must have the same length. If you, for example, use three characters for the first variable that you create, all variables must have a length of three characters.