I'm a bit confused about barometric pressure settings, maybe someone can enlighten me. I know that in the U.S., all airspace above 18,000 ft. is 29.92. On descent however, if you use ATC you'll get cleared to various altitudes with the corresponding barometric reading. I often read that pilots enter the pressure altitude for the landing runway before starting descent. So which method is actually correct? Entering the barometric pressure of the destination airport (meaning just one input for the entire descent), or adjusting it repeatedly with ATC reporting various pressures on each leg of the descent? Thanks in advance for your help.

ATC reporting

This should help !http://forum.avsim.net/topic/356221-qnh-and-ap/Fred.

You enter landing airport QNH in the Descend Forecast page, way up in cruise. You then dial whatever ATC tells you to on your altimeters.

Thank you very much guys, I now feel fully enlightened. :(