
Explanation:

Scenario: Revenue projections are set at the monthly level and summed to show projections for the quarter.
Box 1: IF
Box 2: ISFILTERED
ISFILTERED returns TRUE when columnName is being filtered directly. If there is no filter on the column or if the filtering happens because a different column in the same table or in a related table is being filtered then the function returns FALSE.
Box 3: SUM
Reference:
https://docs.microsoft.com/en-us/dax/isfiltered-function-dax