Altitude on a Polar s710i

Discussion in 'Cycling Equipment' started by Roadie_scum, Aug 29, 2004.

  1. Roadie_scum

    Roadie_scum New Member

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    G'day,

    I am having some trouble with the altitude measuring function on my HRM. I have tried recalibrating (entering altitude when I have a ref point), and sometimes it seems fairly accurate, but 80-90% of the time the altitude readings are way off. For example, I did a hilly ride which I know has maximum altitude around 200m and minimum around 10m, and it seemed accurate for the first 20km, but after that the altitude just sat at over 7000m without much change. Reviewing all my training files, it seems to like being at 1506m, 5346m, 7694m and nothing in between. My climbing's not bad, but I think I would notice that much altitude gain!

    I know the altitude function can be a little inaccurate, but this seems ridiculous. Any suggestions would be greatly appreciated.

    Thanks.
     
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  2. Claes

    Claes New Member

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    This is probably not the cause but your altimeter is not absolute, it is relative to some pressure. As long as the real absolut pressure, does not change, it measures the differences in pressure, translated into height, ok. If the absolut pressure changes, your reading over a long time would be off, but just for one hill, the relative height should still be ok. I hope my messy explanation gives you something.
     
  3. Roadie_scum

    Roadie_scum New Member

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    Yeah I thought that would be the case from first principles, and from looking at the Polar website. I think there's more to it though - the discrepancies I get are just so huge! Thanks for the tip though.
     
  4. The Dubliner

    The Dubliner New Member

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    Mine is just as innacurate.

    I've given up trying to work out the absolute altitude at the commencement of each excercise set. I think the relative ascent is reasonably accurate though. I haven't had any wildly innacurate readings.

    I wonder is there too much technology crammed into these things?
     
  5. dtaffe

    dtaffe New Member

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    I discovered (through trial and error) that if I reset the altitude before every ride, the accuracy improves dramatically. Otherwise, my absolute altitude is frequently off throughout the ride. I just figured out my home altitude (easy, because I live a mile from the ocean), and make resetting part of my preride checklist.
     
  6. Roadie_scum

    Roadie_scum New Member

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    Yeah, this sounds like the kind of thing I need to do. I know my approximate altitude, but when I try to calibrate it it won't let me set the watch below 989m. Any idea what causes that?
     
  7. dtaffe

    dtaffe New Member

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    Make sure your altitude is not negative (ie -989M). I had that problem for a while. I don't know if changing the units to feet makes a difference...
     
  8. techboy

    techboy New Member

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    Yeh, totally! I have to reset the altimeter before each use because it 'drifts'. I think almost all non-GPS based altimeters exhibit that behaviour. Even my analogue altimeter does the same thing. I am not sure why you cannot reset the watch below 989m though. Perhaps a system reset is in order?

     
  9. Roadie_scum

    Roadie_scum New Member

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    Any idea how I would do that?
     
  10. jcjordan

    jcjordan New Member

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    Easy. Just go into the options menu and got to the Altitude area and check the starting height. make sure the Polar is on the bike mount as it wont work when its on your wrist as you block the wholes.
     
  11. Roadie_scum

    Roadie_scum New Member

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    I have done that. It won't let me set my starting altitude below 989m.
     
  12. techboy

    techboy New Member

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    Umm..well, on a 720i, which I don't think is all that different from a 710, there is a reset button on the right side - it's a tiny deeply recessed switch. You would use a paperclip or something to depress it. Maybe I'm talking out of my rear end here...but give it a try! It would likely reset all of your settings back to defaults. :eek:
     
  13. lanierb

    lanierb New Member

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    No question: your s710i is defective. There's no other explanation for a deviation of 7000m. My s720i changes by AT MOST 50-100m, and that's over days of not being used. Over a single day it is usually accurate to within 10m or so. I even have one 30k ride I do frequently where it often gives *exactly* the same number for total ascent: 312m.

    CLB


     
  14. armchair_spacem

    armchair_spacem New Member

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    Yep - as I understand it the thing works on relative atm pressure - you really need to recalibrate for every ride, to account for daily (and intra-day)changes in barometric pressure. The alt and temp functions also suck up memory and battery life something fierce, especially if you're sampling at 5 seconds.
     
  15. Sindoe

    Sindoe New Member

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    Like you, I have had a lot of technical problems w. this specific feature of the Polar s710 watch and so far I have learned that rule #1 is: Calibrate your watch before every ride.

    So unless you live on the top of a mountain (I'm from flat Denmark, so this is not a subject 'round here) how about just calibrating your watch to zero [0] before every ride? Given that your watch is functioning properly, you should get the precise number of climbing meters from each ride, and I gather that this is the info. you want, right?
     
  16. Roadie_scum

    Roadie_scum New Member

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    Yeah, my issue is that when I try to calibrate it, the watch won't let me set altitude below some kind of (seemingly) arbitary figure. I live at about 20-30m, and it won't let me set below, say, 989m.
     
  17. Sindoe

    Sindoe New Member

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    Okay, then you should return the watch to the LBS and get it fixed (or get a new one) :rolleyes: Clearly, there's something wrong with that specific watch.
     
  18. Weisse Luft

    Weisse Luft New Member

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    Barometric altimeters rely on a sealed pocket of air as a reference pressure. Since pressure in such a volume is a function of temperature, there is a temperature compensation module provided. If the temperature sensor cannot read, the pressure has no meaning. Does the temperature function of the HRM/computer work?

    Remember, all barometric altitimeters require a before use setting. In an airplane, you set the altimeter before take off. So is the same for your 710. The reason is the change in density is not linear but rather a function of the altitude. Unlike a Bourdon tube depth gauge used in SCUBA where water is incompressible, air is compressible.
     
  19. alfabenk

    alfabenk New Member

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    Hi, I am having the same problems. When i first started using the 720i it was giving reasonably accurate readings (depending on atmospheric changes) but just recently it swings from 7248m to -480m and just about anything in between. I have tried to reset it to 0m, but it wont let me put in a reading below 6890m. I have tried the reset button, with no success.

    Has anyone else had this problem and know how to fix it?

    or should we be sending the thing back to polar?
     
  20. Odnis

    Odnis New Member

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    It is possible to adjust the odd measurings in your Polar SW. Choose "Edit pulse data" and go to "Height". Choose an appropriate height and, finally, press OK. That way you graphics are calibrated to the "real world", never mind the dumb figures on the watch's display :)
     
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