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

[Richard Bronosky]

Jim has the right idea here. Those altimeters are not intended to give you
super accurate static altitudes. Their purpose is to give you accurate
deltas. If you go hiking or skiing you will know how much you've descended
within 10ft. But, you are unlikely to ever know your specific altitude
within that margin.

Sent from my Samsung Galaxy S3 using the Swype software keyboard.
--Richard Bronosky
On Feb 26, 2013 7:30 AM, "Jim Lynch" <ale_nospam at fayettedigital.com> wrote:

> On 02/25/2013 11:59 PM, Sean Kilpatrick wrote:
>
>>
>> The civilian rade GPS units by and large only claim to be accurate within
>> 50 feet or so -- in any direction. That certainly was proven true during a
>> recent trip to Amelia Island, Florida -- just north of Jacksonville.
>>
>> the unit reported elevation on different days between -50 and +75 feet,
>> when the car was parked ~maybe~ eight feet above mean high tide.
>>
>>  I agree, my sailboat varies from being a  submarine to a low flying
> aircraft when I'm on the water according to the gps.  Also the mathematical
> model of the earth GPSes us doesn't not accurately describe the actual
> surface of the earth.
>
> There are a number of surface models, including sphere oblate spheroid,
> ellipsoid, geoid and others.  Each has it's accuracies and inaccuracies.
>  To compound matters, the actual surface of the earth constantly changes
> its shape.
>
>
> It's best for hiking to use the altimeter as a relative measuring device.
>  "I am ascending" or "I am descending" or "This hill is 50 feet higher than
> my house".
>
> Jim.
> Jim.
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