OK. Just went outside to measure 3 diff. etrex units at our joint.
With four strong sat. signals here's the variation bet. units (I'm
not sure how to do averaging):
Unit one: Accuracy 49ft. Elev.: 423 ft., N38 22.482, W122 31.598
Unit two: Accuracy 47ft. Elev.: 521 ft., N38 22.451, W122 31.481
Unit three: Accuracy 44ft. Elev.:459 ft., N38 22.499, W122 31.635
So, where the hell DO we live? Somewhere in between, I suppose.
BK
>Wild Sanctuary wrote:
>>
>> Curious, then, why two different Garmins (etrex units) gave two
>> different readings (altitude and location) from the same position.
>> Has the Clinton order been rescinded? We were in the open, and were
>> getting signals from 4 different satellites.
>
>No, the order is permanent. The military still has the ability to mess
>it up for selected areas of the world, but currently I don't think they
>are using that at all. And in any case would not for the US.
>
>4 satellites is bare minimum for accurate readings, particularly for
>altitude. One that was slightly off in it's internal clock or location
>data can create quite an error. That's what WAAS is for, transmits the
>error corrections on the individual satellites.
>
>It would also depend on the position of the 4 satellites. Wrong
>combination (all in a small part of the sky), and the error will go up.
>For that matter, did you have the two extrex in the exact same position
>and orientation? It's more than just reading different, the satellite
>signals vary with location. And, of course reflections vary. That's not
>a big issue, but can sometimes throw one off.
>
>Did you use averaging? If you are getting this sort of error
>consistently with averaging, then I'd worry that one of the extrex or
>both had problems. That's way more error than normal. I routinely have
>certain points (like my house) I recheck with mine to make sure they are
>functioning normally. Electronics can go bad, though these things are
>pretty dependable. Repeatability of my house point location with
>averaging over several years has been within 50 feet. And that's with
>the old 12XL and includes before the Clinton order. Lately it's been
>staying within a even tighter circle.
>
>I've not used that model, so have no direct experience with it's foibles.
>
>Walt
>
>
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--
Wild Sanctuary, Inc.
P. O. Box 536
Glen Ellen, California 95442-0536
Tel: (707) 996-6677
Fax: (707) 996-0280
http://www.wildsanctuary.com
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