I was clean up the storage of my macbook pro in these few days, and I find that there is an unknown problem as follows : What I have seen in About this Mac, it said that I used 752.03GB. In the disk utility, I have got 764.27GB used. But when I right click the Macintosh HD in Finder, I have got 488.96GB used in info. Also I have using the app DaisyDisk to make sure the result, and what I have got is used 764.2GB. But the main point is when I calculate the numbers below with the web2.0calc.com, what I have got is 480.8GB. Amazing! I have really confused about this and I hope to know how much storage I have actual used and delete the useless files.