ok if it takes 10 / 20 / 50 / 100 or how ever many to move from Hack to Am to pro to tour pro.
did you notice the first ranked game you shot changed the average on Hack Tier, moved ever closer to Am tier, then after you hit Am you moved towards Pro then you will move to Tour Pro.
When the change from Am over to Pro takes place you get moved back a Tee Box by moving back a Tee box your average will go back up, because it is harder to get to the green forcing more strokes. There is a topic here on the forums where it mentions the tiers reset which makes your average go up.
If it takes X amount of ranked rounds to get an average but the amount of ranked rounds played is below the X amount there is not enough rounds low or high so all of them get used for that tier. It happens to everybody get the ranked rounds in quick the average comes back down soon is the only way to lower it.
TAKEN FROM WGT HELP SECTION
Advancing to the next Tier requires a qualifying Average Score AND a minimum amount of completed stroke play games, which will take a little more time but will help players reach the Levels necessary to unlock upgraded equipment that is helpful to compete at higher Tiers.
link to that information http://wgt.com/help.aspx#tiers
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"Dianne81 / posted
OP statement was incorrect... you will reach a saturation point in each tier where bad scores no longer impact.... but for first XXX rounds when you get to new tier ( maybe 50 for master, or 300 for legend, I really dont know the number) until you get to that point, bad rounds Will negatively impact your average.
Originally poster most likely has reached that saturation point for his pro tier, but when he moves to tourpro tier for first XXX number of rounds, his average will go up and down with good and bad rounds." - - - - - - - - - - - she is correct when you read this topic mentioning saturation point / you will come to a point where it is very high which means it will take more ranked rounds to bring down a bunch of bad rounds average score.
you can get to this topic at the link listed - lots of good info from players in those upper tiers, mentioning the saturation point could be above 500 games in the Legend Tier.
Topic from higher level players chatting over Legend Tier and Average http://www.wgt.com/forums/t/48271.aspx