Xorcist

So I ran an analysis today, saw a fragmentation of about 23%, ran a defrag to completion (0% fragmentation), then immediately did another analysis and saw a fragmentation of 12%. Well 12% != 0% so what exactly is going on? Re-defragging doesn't seem to change the numbers all that much, but it always ends with a 0% yet an immediate re-analysis will yeild a result greater than 0%. So I'm assuming I'm not actually degfragging anything...