ranking question

hey guys, I was just wondering about the ranking system,and was wondering if someone could just confirm? I feel like I see so many people talking about being rank 1 etc etc but I feel like it fluctuates sm! my understanding is that it's for each unit? so vcaa recueces a score for the unit as a whole? from that, for eg if you had person a who was rank 2 with a 90 for two sacs and then there were diff rank 1s so that person a had a higher unit 3 total, would they actually be rank 1? sorry I feel like this makes no sense but if anyone knows that would be great