Change Drop downs to populate multiple values into other cells or return a value of 0

OK. With regard to excel you have to be exact with relationships.

Trying to follow your logic I created an array on the DATA Sheet. It is highlighted in blue.

Hopefully this will give you an idea of how to use something like this in your calculator.

The formulas in columns Q:W multiply the Column O value with the 1 or 0.5 in the Data Sheet blue array.

See the attached example:

Hope this makes sense and is helpful.

Cheers