mine was 7th among 54 waiting almost 2 months before and now when I checked again few days back it said 8th among 508 waiting

mine was 11th among 41 last month now is 12th among 45

don't go by lawfully, you should go to USCIS and sign up for an online account.

That's among people who signed up on this app only. Your rank goes up (decreases) if people ahead of you get approved. It goes down (increases) if people who are actually ahead of you signed up on this app after you did. It's pretty random and useless unless a lot of people with the same case as you sign up on this app. In the ideal scenario, your relative rank on this app (rank divided by the total number of people in line) would be approximately the same as your actual relative rank at USCIS.

@Zaki Z thank you for the explanation.

@CC B does uscis provide any information except for case status?