Question On DB02

Hi all,

On Netweaver 04 BI, I type the transaction DB02, after which, I click on the button which says

"Space Statistics", I get on to a page which gives me a Tablespace history, In this page, I can see something called Chg/day, Can anyone please tell me what this Chg/day mean, and how much on an average it should be, And what do you mean by saying extents are, please take out some time and be brief about it.

Thankyou

SreekuL NaiR