I believe there is a problem with the decrement operator.

http://www.artemisgroup.com/test.php

$percentchange = .30;
while ($percentchange > -1){
  $percentchange -= .01;
  echo $percentchange;
}

zero is returned as -1.422473250301E-16 and 0.01 is returned as 0.0099999999999999. This seems incorrect to me.

Thanks