PokerTracker Aggression Factor help

I have just purchased PT3 after using it for the trial period and a bit during beta testing. I don't quite understand the aggression factor stat. I think the higher the number the more likely to bluff but not sure if that's totally true. I know that I got into a good run of cards during a tourney a short while back and had a AF of 19 with little bluffing. I guess my questions are; What exactly is the AF? How do I correctly use this stat? Is there a minimum number of hands before this stat becomes accurate? Any other relevant info?

Aggression Factor is calculated as -

Bets + Raises / Calls

The more I think about, the less relevant this stat becomes. It isnt really a measure of how aggressive a player is, but of how likely they are to call. You don't have to bet or raise a lot to have a high AF, you just have to call very rarely. The only thing I see this stat being an indicator of is recognizing when very passive players have a big hand.

This is why I find myself using the AgF or Aggression Frequency stat much more now. This is a measure of how often a player takes an aggressive action rather than a ratio of aggression to passivity.

AgF is calculated as -

Streets where an aggressive action was taken / Total Streets Seen

expressed as a %

Quoting from Beginners Guide to PT

"Aggression Frequency (times_bet + times_raised) / (times_bet + times_raised + times_called + times_folded)

Aggression frequency will return a percentage. The higher the percentage, the more your opponent is betting or raising. The more they are betting and raising, the more it is likely that they are trying to buy a pot.

When you see a player that has a high agg. factor (roughly over 2.5) combined with a low agg. freq (under 35%) - when they bet, they have a hand. Do not go up against this player in this situation unless you have a monster. "

Thanks guys. As I mostly play SnGs and MTTs, I'm thinking that the aggression factor is probably not one of the more useful stats. I have seen the AF displayed as infinite after many hands and think that there has to be a pretty big data base on a player before the stat is accurate. And as far as aggression goes preflop, I think that can easily be seen when looking at VP$IP and PFR stats. I will take a look at the frequency stat and think that might be useful after the flop.