Dear Troy,
First of all I am impressed you posted such a coherent response post in the middle of the night. Yes I am well aware my reply to you was 'pointy headed', but after midnight is not the best of hours to allow such posts to sink in. Given your history exam result of 80%, I will take your recollection of your maths result of 18% as accurate. However, we are talking 30+ years ago here! Odds on the pointy head exam marker that gave you that 18% maths grade is now dead, so I would put all that out of your mind if I were you.
Given you have learned the lesson of compounding interest since then, as evidenced by your doing OK in the investment markets since, I hereby award you the 'Sharetrader Maths Certificate' for your prowess in mathematics in the real world. So as a now qualified mathematician, you will be in a good position to understand the less pointy headed version of my previous post.
1/ My complicated formula is really only a version of the compounding interest effect.
2/ The compounding interest effect doesn't work properly if you conveniently forget about extra money you put in along the way (as I did).
3/ The amount of compounding interest you get will be affected if you pull money out along the way (for example dividends).
If you understand those three statements, then you understand what I was getting at with my 'pointy head' formula.
SNOOPY