help with triggers please!!!

[fvd]

Hi,

I'm making a new mission (hope to share it with you in a couple of days).
But i need some explaining about triggers.
I made a map zone, once you enter this zone you should receive a radio message.
The window of the trigger for this message has got some options i don't understand and don't find any info about.
-Area Presence: here you can choose between "NotContinuous" and "Continuous"
What is this?
And second:
-Patrol time (min): here you can enter a value in minutes.

I assume it has something to do with the mapzone, but what exactly?

Thanks already!
Regards,
fvd