[ale] WAY [OT] but geeky - how do I calibrate GPS barometric altimeter

[Randy Hagan]

You could try to use the Altimeter (Barometric pressure) setting for 
the closest airport.  We use the pressure value on the altimeter to get 
accurate altitude.  We adjust it as we fly do different areas to ensure 
we are at the right altitude (Under 18,000 FT anyway).  You could check 
the Cherokee and Gainesville Airport weather observations.  They would 
probably be about the same.  If you know how to read METARs you can get 
the barometric pressure.  If not, look for the four digit number after 
the first A.  That tells you the altimeter setting.  Example:  261455Z 
AUTO 10007KT 2 1/2SM RA BKN003 OVC007 03/01 A2963 RMK AO2 TSNO.  The 
A2963 is the Altimeter (or barometric pressure) setting.  IT's 29.63 in. 
29.92 is standard pressure (which doesn't happen much).  You can check 
the weather at airnav.com.  Just click the airport tab, enter the 3 
letter identifier (CNI is Cherokee, GVL is Gainseville).  Scroll down 
and look over to the right side and you will see METAR.  They take them 
every hour (The example above was taken on the 26th at 1455Z - or 9:55AM 
Local).  I'm not sure how accurate you GPS will be, but it should get 
you close.  I think for every inch of mercury you are off, you 
increase/decrease altitude by 1000 feet.

Regards,

Randy



On 2013-02-25 20:07, Ron Frazier (ALE) wrote:
> I don't think Cumming has an airport, but I'll keep it in mind.
> 
> I took the GPS out with me to supper.  When I left, my house was at
> 1210 feet above sea level.  By the time I got back, it had sunk (on
> the display) to 1170 feet.  In the last 20 minutes of me sitting here,
> it has raised back up to 1185 feet.
> 
> So, I guess I cannot expect too much from the elevation function of 
> this device.
> 
> Sincerely,
> 
> Ron
>