You can duplicate an item on the shelf, and then re-use it for another calculation or for placement on another shelf of the visual.
To duplicate, follow these steps.
When creating or editing a visual, determine which field variable you must duplicate.
The shelves that support the alias option depend on the visual type, and are typically available for X and Y axes, Measures, Dimensions, Colors, and Tooltips.
Click the icon to the right of the variable.
A copy of the field appears on the same shelf.