Thank you for your answer.
It is most likely me who isn't able to express the question correctly. But, I want to compare my calculated field to the original data and not replace it.
I have a list of previous projects which I have displayed in graph like the one below, which I want to compare to the new project. Since the new project is calculated on behalf of the previous projects, then Tableau won't let me display the new project as the calculation is connected to the original data. The image below illustrates how I would like the new project to appear.