What are DACs in Power BI? What is the difference between a calculated column and a calculated measure?

DACs in Power BI most likely refers to DAX, the Data Analysis Expressions language used to create calculated columns, measures, and calculated tables. A calculated column is evaluated row‑by‑row during data refresh and its result is stored in the model. It can be used in relationships, filters, and slicers, but because it is static it can increase the size of the model. A calculated measure, on the other hand, is evaluated on the fly when a visual is rendered, based on the current filter context. Measures are not stored in the model; they are computed at query time, which makes them more efficient for aggregations. The key difference is that calculated columns are pre‑computed and persist, while measures are dynamic and context‑aware. For example, you might create a calculated column to flag products that exceed a target price, and a measure to sum sales across all products. DAX provides functions like SUM, AVERAGE, CALCULATE, and FILTER to build both types of expressions. Understanding when to use a column versus a measure is essential for model performance and correct reporting.