A calculation is often referred to as a calculated field in Tableau. This is because, when you create a calculation, it will either show up as a new measure or a dimension in the data pane (unless it is an ad hoc calculation). Calculations consist of code that references other fields, parameters, constants, groups, or sets, and use combinations of functions and operations to achieve a result. Sometimes this result is per row of data and sometimes it is done at an aggregate level. We'll consider the difference shortly.
There are multiple ways to create a calculated field in Tableau:
Navigate to Analysis | Create Calculated Field... from the menu.
Use the drop-down menu next to Dimensions in the data pane:
Right-click an empty area in the data pane and select Create Calculated Field.
Use the drop-down menu on a field, set, or parameter in the data pane and select Create | Calculated Field....
In Tableau 9.0 or later, double-click an empty area on the Rows, Columns...
