Maybe there is an easier answer. If my "core equity" is 1% of my uncommited money, and the trading interface tells me how many units I can purchase, then can't I just take 1/100th of that number? I would still like to understand the math, though, lol.
http://www.fxstreet.com/nou/content/107410/content.asp
"If you want to enter a second position then you should calculate 1% risk of your core equity not of your starting balance!"