When you had registered for the challenge and got the participation POAP, we had send you a participation number (XXX#). This number corresponds to one of the numbers in one of the charts. Every day we gather data from beaconcha.in, who sponsored us an access to their API  for this challenge, to see if your validator managed to have less than <2 missed attestations. If your validator manages to do it, he will move up one step to 30. 

This means a S-Tier performing validator will reach the top at the end of the month!
Performing perfectly makes your validators eligible to get the S-Tier POAP and win the prize.