How to compare 2 columns from different tables when they aren't primary keys in the relationship?

[mafioso]

This is what my table looks like:

My primary key is the KSt_Idx field in both tables. Now I want to connect both Time Periods in order to show the difference between the values in a chart. I'm pretty new in Power BI and that's why I don't know exactly what to do. Is there a way how to filter by date (so if I choose March) that in both tables just the march values are shown? The structure of the Time Period field is in both fields the same and contains the same values. 

[v-chuncz-msft]

@mafioso,

You may take a good look at this discussion.

http://community.powerbi.com/t5/Desktop/Relational-Date-Filter-By-Other-Date-How-To/td-p/298373