What is a Level of Detail (LOD) expression and how do you use it in Tableau?

A Level‑of‑Detail (LOD) expression in Tableau lets you aggregate data at a granularity that differs from the view. The three types are FIXED, INCLUDE, and EXCLUDE. FIXED locks the aggregation to the specified dimensions regardless of the view, INCLUDE adds dimensions to the aggregation, and EXCLUDE removes dimensions. For example, SUM([Sales]) FIXED [Region] returns total sales per region even if the view shows sales per city. LODs are powerful for creating calculated fields that need consistent granularity across filters and for avoiding double‑counting when multiple dimensions are involved.