How do they know the length of my trip ?

[Fabio]

Lets say that I go abroad with my AP, and I stay for 4 months. How would they know that I was out of the USA for 4 months if they dont check anything when you leave ? The INS dont check anything when u leave the US, right? They only do check it when you come back , dont they ? If so , they cant say the lenght of your stay abroad... Can somebody explain that to me ?
Its a bit confusing.
Thanks for helping...

 

[jaxen]

Anybody who knows how to read a passport...

will know how long you have been out. You might get lucky if there is a big waiting line. Some officers (most probably to make an conversation) ask how long have you been out of US? There is no confusion in this issue. It is a precautionary measure and not a rule. I am not aware of any official rule on this and I strongly believe that you can be out of US and enter just a day before the expiry date and you will still be admitted.