My CFC has a goal of 1X a year with the full work-up and every 3 months for just a spirometry.
One time I was questioning how you tell your lung volume on this board, because I thought that the spirometry doesn't measure your actual volume, but rather measures the amount of restriction or obstruction. Not that it matters, because if you're obstructed, you can't use all of your volume anyway, but that's another thread....
Anyway, "someone" here sent me a PM along with the following link that was very helpful for me. It explains the "box" test and what it measures.
<a target=_blank class=ftalternatingbarlinklarge href="http://en.wikipedia.org/wiki/Plethysmography
">http://en.wikipedia.org/wiki/Plethysmography
</a>