Someone correct me if I'm wrong but i believe the number 2992 is the standard airpressure.  This is what your altimeter should be set to inorder for a correct reading.

The altitude in question is called transition altitude. It's 18,000' in the continental U.S. and as low as 3,000 in some countries(Cuba for example). When the controller says "altimeter 29.92" Par8', he is giving you the current setting that should be entered in  the Colesman window(the small window with four numbers on the altimeter). Your altimeter uses PRESSURE to determine your current altitude. Pressure changes with temperature and variations in weather. If you fly over a long distance,and the pressure changes quite a bit  , your altimeter may be hundreds of feet off. In this case, you would want the correct altimeter setting, or you may be higher, or much worse, LOWER, than the altimeter indicates. The standard M$ program defaults to 29.92", which is known as standard pressure. You can change the pressure on the defaults, or like Will says, if you download realtime weather, you will have the controller tell you something other than " altimeter 2992".

I'm from south Florida, I got it the first time, I'm just too lazy to type the whole thing out!