Boost Guage and Barometric pressure

[awdturbo]

I would like to know how many people see this problem.
I think it is from Barometric pressure but here is the problem:
At home when the car is off, the boost is right smack in the center.
40 miles away (at work) the needle goes down slightly below 0 ????

 

[L2RTSiAWD]

What type of gauge is it?


Later,

 

[awdturbo]

Autometer 30-0-30 Boost Guage Phantom Series