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first km inaccuracy

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  • first km inaccuracy

    Since the day it arrived in March, the 645M has been the best device I've ever owned. We've run about 400 miles together without issue and it rarely leaves my wrist.

    Just recently I've been frustrated by inaccuracy during the first km. I've been running for enough years to have a pretty good feel for my pace and certainly good enough to know the watch is showing me a min per km slower than I am likely moving.

    It sorts itself out before the first km is up, but it's pretty frustrating.

    I remember my old 310XT used to do this and I learned to delete all the onboard run data and it would be fine (though as a former software developer, I could never understand the logic of that - but hey, it worked). I don't remember this problem occurring with the FR630. I duly deleted the activity data on the watch, but it isn't resolving the issue.

    Has anyone else experienced this and have any tips to share?

  • #2
    The obvious question...Are you waiting until you have a good GPS signal before you start?

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    • #3
      Originally posted by philipshambrook View Post
      The obvious question...Are you waiting until you have a good GPS signal before you start?
      I find that obvious questions are only obvious to some! I've certainly had my share of "doh!" moments. But yes, I think so.......I wait until it tells me GPS is ready and it turns green. This is taking just a few seconds so I am assuming its GPS caching, which make me wonder if the problem is there somehow???

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      • #4
        Starting with a green GPS indication should be good however, some would suggest you wait for a little longer just to be certain, until the pace field (if you have one visible) show zero. If you are getting a positive indication that your GPS is ready within seconds then the EPO.bin file is likely to be ok. Always worth connecting to Garmin Express to have the EPO.bin file updated though. BTW, inaccurate 1st km wasn't something I ever noticed with the 310XT.

        Might be worth talking to Garmin Support.

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        • #5
          Originally posted by philipshambrook View Post
          Starting with a green GPS indication should be good however, some would suggest you wait for a little longer just to be certain, until the pace field (if you have one visible) show zero. If you are getting a positive indication that your GPS is ready within seconds then the EPO.bin file is likely to be ok. Always worth connecting to Garmin Express to have the EPO.bin file updated though. BTW, inaccurate 1st km wasn't something I ever noticed with the 310XT.

          Might be worth talking to Garmin Support.
          thank you - I shall do that

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          • #6
            I also see inaccuracy on the first lap, especially under some tree cover - things I did not encounter with the 630. I do wait quite long after the 2D fix has been obtained.

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            • #7
              Originally posted by talsela View Post
              I also see inaccuracy on the first lap, especially under some tree cover - things I did not encounter with the 630. I do wait quite long after the 2D fix has been obtained.
              Thanks for the reply. I'm struggling to figure out why this has just started to happen to me. I am getting older, perhaps I'm kidding myself about my pace

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              • #8
                sjbrain I don't think so. I also see issues with first km and also with the very basic accuracy on this watch in general.
                Today I followed a course I set on GC. The course measured 18.88km on GC, the watch measured 18.5km (over 2% divergence). What bothers me more is that lap pace is totally undependable - within a single 1km lap, it varies all through (even at 900m, when average lap pace should be quite "heavy") between 3:40 and 4:15, and moves as much as 10-15 seconds, which is not possible. I'm a very steady runner, and my 630 reflected that. With the 645 lap pace seems almost random.

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                • #9
                  I've dug the 630 out of the back of the drawer and charged it up. I'm going to do some more runs wearing both and see what's what.

                  following a suggestion here, I have waited around after GPS goes green a few times this week and it does seem to make a difference - but a sample size of two isn't enough to conclude.

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                  • #10
                    Waiting for a "green" GPS will usually make a difference, as up to that point, it's still figuring out exactly where you are, so distances/speeds/etc could be a bit odd up to the point it gets a good fix.

                    In my CIQ apps, I don't even allow the user to start recording until there is the equivalent of the green GPS for that reason.
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