After 4 days getting to grips with P2A Ihave decided its a must addon, i had my first A to B flt with Sid's, star's, approach but 1 problem all of a sudden iam being told about QNH and NOT the usual Alimiter 29.30 which changes often.  Is it a USA thing  setting, i tried tunening 29.30 down to 10.30 in flt had to stop that plane went into a step climb..lol any advice guys  thanks

This is the barometer setting on your altimeter at ground level up to the transition altitude (18000 in the US) it should be set to the actual barometer on the ground. When you go past 18000 ft set it to the standard pressure of 29.92 inches or 1013 hPa. When descending through 18000 ft. find the barometer reading at the airport you are going to land at. If you display the Map (m key) you can find the airport and right click it. Or go to a website where you can search on the Metar for an airport get it from there.

On 01/02/2018 at 11:11 PM, steve1919 said:

it should be set to the actual barometer on the ground.

No, that would be QFE (the pressure measured at the airfield datum). QNH is effectively QFE adjusted to MSL using the standard atmosphere and gives elevation above MSL.