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

[Ron Frazier (ALE)]

Hi all,

I just got my hands on a neat Garmin Etrex Vista H handheld GPS on 
clearance for hiking trails and such.  It has a barometric altimeter 
that I wish to calibrate.  I have to either enter an accurate known  
barometric pressure; or I have to enter an accurate known elevation.

I've checked Weatherbug (for Cumming, GA), The Weather Channel, and the 
Firefox ForecastFox plugin.

The barometric pressure readings are: 29.85, 29.92, and 29.90.  As I 
understand it, these variations would be enough to create altimeter 
reading differences of around 70 feet.

I can't necessarily use my weather station as a good barometric pressure 
gauge, since it depends on elevation.  (I usually calibrate that 
instrument by putting in the barometric pressure from The Weather Channel.)

I don't know the exact elevation of my house, nor the exact elevation at 
the trail at the park.

I can calibrate to GPS elevation, but that's not very accurate.

Garmin says the altimeter is accurate to 10 feet if properly 
calibrated.  Of course, it will change with the weather.

So, how can I determine accurate barometric pressure for a location, or 
accurate elevation, so I can calibrate this thing?  Is there a way to 
get elevation from google maps, or something?

Note, this is not critical, not life threatening if I don't find the 
answer, not even exceedingly important.  But, I just want to get the 
most usage out of the device that I can.  And, you guys are a great 
source of geeky information of all sorts.

Any help, as always, is appreciated.

Sincerely,

Ron


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Ron Frazier
770-205-9422 (O)   Leave a message.
linuxdude AT techstarship.com