Stackdriver - arithmetic operations between queries

Hi there,
I would like to monitor our GCP Total disk size in a Singlestat Panel to get notified when there is a too big growth and put thresholds accordingly. I need to use the growth because the size of my DB has a natural linear growth due to telematic data.
Therefore I would like to compute a ratio between two stackdriver queries:

  1. average size in the last hour;
  2. average size in the last week

Any idea if it is possible to compute a ratio between two stackdriver queries ?

Thank you for your help