Hello,
We have been collecting NPS data from external webpage, and we get a ticket to our system every time someone give NPS rating.
These tickets are marked with tags: nps_0, nps_1 etc.. there is also "Drop-Down" Ticket field named "NPS" made. 
I have been struggling to make a NPS metric with explore, so we would get NPS result in monthly basis. What I managed to do is the picture below, but moving forward I would require some help.

So what I think would be required is to:
- count tags nps_0 to nps_6 (detractors) per month
- count tags nps_7 to nps_8 (passives) per month
- count tags nps_9 to nps_10 (promoters) per month
then it would be needed to do the math to count NPS:
- detractors / all results =
- promoters / all results =
Once this would be calculated, last math to do would be to have promoters - detractors to have NPS score.
I would be very grateful if someone could share ideas for this, and if there is any helpful articles I'm willing to read. I tried to search but could not find solution myself.

