Garmin GPS III+ altimeter calibration

[Guest 3Lushs]

Can anyone help me calibrate my altimeter. I don't think I've done it correctly. I'm not really sure how to do it. I've never really needed it but would like to know if it's working properly.

 

Thanks,

John

[Guest k2dave]

sing barometiric altimeters that needs calabration sometimes several times a day - is worth the error

[Guest 3Lushs]

Thanks alot. Have you been pleased with yours? I really like mine but haven't used it extensively.

[Guest gstrong1]

I agree with k2dave. I always take out my III Plus,my MAP76 & my Vista on cache adventures, & the MAP76 & III Plus elevation readings are always within 30 ft. or so of each other. But the Vista, which I believe relys on barometric pressure, is almost always off by at least 100 ft. If I recalibrate the altimeter on the Vista, entering that I don't know the elevation or the present barometric pressure,and entering yes when it asks me if I want to use the present elevation, it usually gives me an elevation that is very near what the MAP76 & the III Plus have given me. I don't quite get it. If it already knows what the elevation is,why screw around with barometric pressure. I'm sure there must be some scientific reason for it, but what good is it, if later on in the day, I have to go through the recalibration process again. So I usually don't take any elevation readings off the Vista. The III Plus is for sure my favorite unit of the 3 for geocaching purposes, at least until I get the V.

 

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Gary "Gimpy" Strong

Rochester,NY

[Guest Cape Cod Cache]

You should be able to force altitude while in 2D mode, like right after you start it up. I can do it with my GPS48 and 126. Both are used at sea level, so I'd don't use it, but it helps with accuracy. I don't want to see negative numbers, but I'd probably know I was sinking anyway.

[Guest Prime Suspect]

quote:

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Originally posted by gstrong1:

I agree with k2dave. I always take out my III Plus,my MAP76 & my Vista on cache adventures, & the MAP76 & III Plus elevation readings are always within 30 ft. or so of each other. But the Vista, which I believe relys on barometric pressure, is almost always off by at least 100 ft. If I recalibrate the altimeter on the Vista, entering that I don't know the elevation or the present barometric pressure,and entering yes when it asks me if I want to use the present elevation, it usually gives me an elevation that is very near what the MAP76 & the III Plus have given me. I don't quite get it. If it already knows what the elevation is,why screw around with barometric pressure. I'm sure there must be some scientific reason for it, but what good is it, if later on in the day, I have to go through the recalibration process again. So I usually don't take any elevation readings off the Vista. The III Plus is for sure my favorite unit of the 3 for geocaching purposes, at least until I get the V.

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What you've probably done is screw up the Vista's calibration. GPS altitude calculations are terribly inaccurate. But if you've got two GPSs next to each other, from the same manufacturer, they're going to be looking at the same satellites and probably using the same calculation algorithm, so yeah, they're going to come up with similar numbers. That doesn't mean they were right. Chances are, the Vista was probably far closer to the correct altitude. But you told it to ignore its barometric readings and rely on GPS calculations. No wonder it's giving you whacked out reading. I would suggest doing a hard reset, and seeing if you can't get it back to its factory settings.

[Guest k2dave]

quote:

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Chances are, the Vista was probably far closer to the correct altitude.

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Have you ever used a barometric altimeter? They are a pain in the @$$. If air pressure changes just a little you could be off by hundreds of feet. The accuracy of the gps altitude is accurate enough for most purposes. The vista is giving you the incorrect reading because the air pressure has changed - this is totally normal - that's why you have to calabrate it (usually more then once/day)