This is way off-topic on this response, but in this day and age of
e-mail list archives ending up on Google...

Dave... you're going to end up hurting someone if you use 29.92 every
time you're IMC like that.

You're actually supposed to use the closest known correct altimeter
setting to your location.  And ATC has requirements to make sure that
you have that setting if you're in the IFR system unless you're in
uncontrolled airspace (rare even out here in the "West" anymore), then
it's the Pilot-in-Command's responsibility to get.

I'm too lazy to go to the basement to get the FAR, AIM, and Controller's
Handbook references right now, but please... don't just use 29.92
blindly.

You're friendly neighborhood aviation safety warning guy...

Nate

On Wed, 2002-09-04 at 15:46, Dave King wrote:
> >If I am driving up a mountain and a storm is approaching then what? The
> >pressure drops from the storm and changes the
> >barometric pressure changing the altimeter, which is changing because I am
> >driving up the mountain.
> >
> >The MPX4115A is calibrated and compensated. Then pressure measured is
> >correct, so how do I know when the change if from
> >the altitude or a storm? If I am not moving then no problem. The altitude
> >is the constant, If there is no storm then the
> >relative barometric pressure is the constant.
> >
> >Gordon Varney
>
> You can't know what is affecting what. In aircraft altimeters the
> barometric pressure is set to local pressures as you go
> along if you are low level and to 29.92 inches of mercury if you are ifr.
> The idea is that everyone in the same area/altitude
> will at least be using the same base setting and be able to know what
> altitude they are at.
>
> With a fixed station position you can set the altimeter to a known altitude
> and derive the current pressure. With your setup
> unless you have access to a local/regional report or can set it to a known
> altitude its as good as you can get.
>
> Dave
>
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