Newbie question about accuracy

[+Kite and Hawkeye]

I just got a yellow Garmin eTrex and found my first cache yesterday. I was quite pleased with it and had no trouble, even under a fair number of trees. While paging through the stats at the back of the manual, I saw that it said it had an accuracy of "3-15 ft with DGPS corrections, 49ft RMS." Now, I know I don't have an Optional Differential Beacon Receiver, whatever that is, but if accuracy is no better than 49 feet without it, why do I go outside and see "Ready to Navigate, accuracy 18 ft"?

 

[This message was edited by Kite on June 26, 2002 at 09:33 AM.]

[+GOT GPS?]

Garmin has given a general accuracy of 49 feet for their GPS units for years. Your GPS can do better than that out in the open, but worst than that under tall wet trees. DGPS is mainly for people that need the accuracy, and that also is best done in the open. Surveying takes that to a higher level, with and accuracy of inches.

 

My home page about GPS units and information

[+majicman]

quote:

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Originally posted by Kite:

I just got a yellow Garmin eTrex and found my first cache yesterday. I was quite pleased with it and had no trouble, even under a fair number of trees. While paging through the stats at the back of the manual, I saw that it said it had an accuracy of "3-15 ft with DGPS corrections, 49ft RMS." Now, I know I don't have an Optional Differential Beacon Receiver, whatever that is, but if accuracy is no better than 49 feet without it, why do I go outside and see "Ready to Navigate, accuracy 18 ft"?

 

[This message was edited by Kite on June 26, 2002 at 09:33 AM.]

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The "RMS" they are referring to is "Root Mean Square". When you say that house power is 120 Volts AC you are talking about its RMS value (it is 1.717 times that if you are talking Peak, or 2 x 1.717 times that if you are talking Peak to Peak.)

 

But of course, they might also (by RMS) mean:

 

Railway Mail Service.

Royal Mail Service.

Royal Mail Steamship.

 

but I doubt it...

 

--majicman

 

(Always trade UP in both quantity and quality and Geocaches will be both self-sustaining and self-improving!)