The groupings of functions mentioned in the preceding section are important for understanding what kind of functionality is possible. However, the most fundamental way to understand calculations in Tableau is to think of the three different levels of calculations:
Row Level calculations: These calculations are performed for every row of underlying data. For example, you might calculate the number of days between the start date and end date. The resulting value would be calculated and available for each row of data.
Aggregate Level calculations: These calculations are performed at an aggregate level. The view level of detail is defined by fields used as dimensions in the view. You might add or change the dimension in the view, and the Aggregate calculation will be re-calculated to give the result at the new view level of detail.
Table calculations: These calculations are performed at an aggregate level on the table of aggregate data, which...