switch() syntax

Reporting Amount Base_PL =
SWITCH (
    [Selected Currency],
    1, [Group Currency Amount Base_PL (EUR)],
    2, [Company Currency Amount Base_PL],
    3, [Budget Currency Amount Base_PL (EUR)]
)

Jeanxyz based on your question this is where the condition is getting checked:

Reporting Amount Base_PL =
SWITCH (
    [Selected Currency],   --take the value of selected currency 
    1, [Group Currency Amount Base_PL (EUR)], --if it is 1 return this measure
    2, [Company Currency Amount Base_PL],    --if it is 2 return this measure
    3, [Budget Currency Amount Base_PL (EUR)]  -- if it is 3 return this measure
)

--if none of above condition met, means selected currency is not 1, 2, 3 it will return blank