Need help with DAX IF Statement: Dynamically setting parameter order based on a selected value

In DAX, the equals symbol is used in two different ways. Setting one thing equal to another, and testing for equality. In your FCL Per/Wk measure, the first two equals symbols are setting one thing equal to another and the last 3 are testing for equality. From your description it appears you are imagining that your IF statement is setting the value of [Parameter Order], and it's doing no such thing. It's testing whether [Parameter Order] is 0 or 1 and returning TRUE or FALSE accordingly.

If you want a filter applied to the PARM Time Scale table to affect the PARM FCL Per/Wk table, create a relationship between them in your model. You will need to add another column to your PARM Time Scale table to achieve this (containing 0 or 1 accordingly).