Question on Ghost Automatoc Backups

I did a full backup of my hard drive when I first installed Ghost.  It took 8 hours.  Ghost is set to do an automatic backup every Sunday morning.  Will it take 8 hours every time or does can I set it to do an incremental backup of only the things that have changed since the last backup? 

 

I can't afford to have my computer tied up for that long every week.

 

Any suggestions?

 

Thank You.

 

ALAN