Show a relative measure in a card

Hi all,

I've set in my model a book to bill measure which I measure within a certain timeframe window and this is obtained by dividing two different moving averages.

This is helpfull to see the trends but I would like to show in a card just the value of the book to bill related to the last week.
I use something like BtB=calculate(Booktobill, Week_offstet=-1) but it doesn't show the correct value.

Im afraid that, selecting "Week_offstet=-1") this drive to a reduction of the timeframe of the analysis and return the wrong number for the book to bill.
How can I solve this issue?

Thanks