You can't do arithmetic addition in the field directly. The + operator works as concatentation there. You can utilize a function, though, to do the match for you. I created this function:
def AddValues(num1, num2)
{
num1 = (float)(num1);
num2 = (float)(num2);
return (num1 + num2);
}
It forces each number to a floating point number and them adds them together and returns the value. In this case, you would put this in the TargetSize field:
TargetSize : AddValues(createvolumebin.size_mb, $addedsizebin)
Good luck!
Brian Jones