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47902Re: GPS Routes

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  • mcooprec
    May 2, 2010
      The Suunto doesn't use GPS. Dunno how it stays so accurate. I backpack about 4 to 6 weeks each year and have been in many storms that blow in at different times during the day or night, and my Suunto almost always seems to stay uncannily accurate (although a little less so now that it's several years old, which makes me think the sensor is beginning to degrade). It's highly unlikely that each of those storms produced the same barometric pressure each evening and following morning.


      --- In Zion_National_Park_Hiking@yahoogroups.com, "TomJones" <ratagonia@...> wrote:
      > --- In Zion_National_Park_Hiking@yahoogroups.com, "mcooprec" <coopermb@> wrote:
      > >
      > > Thanks for the explanation, Tom. That makes sense, and I stand corrected. In any case, we both agree that GPS elevation readouts are not to be trusted.
      > >
      > > I agree generally with your observation about altimeters being sensitive to barometric pressure, Tom. (Btw, altimeters also use temperature change -- along with barometric pressure -- to determine change in elevation.) But some altimeters are amazingly almost immune to barometric pressure changes. My Suunto can go through an overnight storm and drift only 20 feet or so (dunno how it does this trick; Suunto are understandably cryptic about their proprietary technology)! My Casio altimeter, on the other hand, will drift 200 feet.
      > >
      > TOM==> Uh, no. Altimeters past the most primitive are "temperature compensated"; which means a temperature sensor is used to correct the error in the barometer due to changes of temperature. Using the lapse rate (the change in temperature due to altitude) would be impossible, as the lapse rate changes constantly with location and time - perhaps an Internet Link to more-detailed weather information that currently exists could use the lapse rate to determine elevation ;-)
      > That Suunto is one SMART altimeter. Perhaps it obtains GPS data and corrects itself. Or figures out when it is not moving and lets the barometer change. Or has gotten used in conditions where the morning barometric pressure is the same as the evening barometric pressure due to the nature of the storm.
      > Tom
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