At the first time, I installed ubuntu 12.04 on my desktop and ran the update manager. At that time, the size of the update is about 168 MB. Then I did something wrong on device installation, so I decided to re-install ubuntu by erasing the previous one. But what I noticed was that when I ran the update manager on the new ubuntu, the total size of the update is now about 100MB, not 168MB. So now I am wondering if there's something broken on the last installation, because the size of the update is smaller than the previous one's...
Please tell me whether this is a fault at installation or I can ignore this and proceed
OK. This is not a fault. I did three installations on the same machine, all without internet connection, and then later ran the update manager. Then the size of the update was identical for every installation. It looks like sometimes, updates during installation from internet differ from time to time, but as a whole, there is nothing wrong with it.