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

[Ron Frazier (ALE)]

On 2/26/2013 11:17 AM, Derek Atkins wrote:
> Ron,
>
> "Ron Frazier (ALE)"<atllinuxenthinfo at techstarship.com>  writes:
>
>    
>> 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
>>      
> The issue is that the barometric pressure is constantly changing.
> Pilots use barometric altimeters, and the rule is that they need to
> reset them every 100 miles or every hour.  An airport will report the
> current altimeter setting every hour, but some automated systems will
> report it every minute, and yes, it can change rapidly if you have
> strong storm systems.
>
> Basically, this is a long-winded way of saying that you need to be
> constantly resetting altimeters.  When they are set properly they are
> very accurate.  However they need to be reset frequently to remain
> accurate.
>
> One tip: the barometric pressure doesn't usually change significantly
> over short distances.  Most of the local airports will have the same
> setting, so you could theoretically just dial the weather at, say,
> Kennesaw (770-425-3406), to get a local altimeter setting that should be
> "close enough" for you.  Worst case you'll be maybe +/-50 feet off, but
> is that really too much error for your use-case?
>
> -derek
>
>    

Hi Derek,

Thanks.  I'll add that phone # to my list of resources.

See also my reply to Randy H.

Sincerely,

Ron


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Ron Frazier
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linuxdude AT techstarship.com