Ratio Calculation between two user-selected columns

Hi all, 

Ref example table below. Various numeric metrics for each month - there are about 30 total columns similar to the examples (events, defects etc.)

I'd like to calculate ratio's between the columns based on user-input - I'm imagining two filters titled Numerator & Denominator. The two filter values are passed to a Measure(?) that then calculates the ratio for each row. In the above example the user would have selected 'defects' in the Numerator filter and 'cycles' in the Denominator filter. That result is then plotted in a line chart over time.

I know I can create loads of calculated columns to do this up-front for all the possible combinations, but was wondering if possible to do this dynamically based on user input?

I've looked at other similar articles but they don't quite fit what I'm after - any help appreciated. 

Thanks