nub theory please help me out

Im new here and very surprised at the nub theory as i just had a baby whois now 7 months old and i hadno idea this existed. I had my NT at 13wk 3 days and was told possibly a girl but the tec didnt seem to sure of herself please any ideas would be nice i dont really understand the nub theory does it go by the fork or the angel or both

The angle! >30 degrees = Boy < 30 degrees = girl! The fork and the bulb can happen on either but from what I have seen the girls more than often have a fork the boys the bulb but it is more the angle because boys can have forks and girls bulbs it has to do with the angle of the scanner!