backing up 14.92 GB????? Why so little?

[0186279]

At the risk of sounding terribly noobish...

Just plugged in my external and time machine says its backing up 14.92 GB...seems awfully small.

Does it only back up whatever has changed since the last update?

 

[sammich]

Does it only back up whatever has changed since the last update?

That.

 

[0186279]

That.

Makes sense, but I feel like the previous times it has backed up the entire HD.

Oh well!