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66S FIT file bug. Exaggerated total ascent.

Hello, using my GPSMAP 66S  to record the activity for a local walk I do often. I have odd results from the 66S.
Here are the symptoms:

  • Actual total ascent is 351m. (Recorded on Epix and it matches the size of the hill)
  • When viewing activity on the 66S it shows total Ascent 799m (descent 800m)
  • When I sync with Garmin Connect the activity shows as having total Ascent of 799m.
  • 66S set to record FIT and GPX.
  • Transfer FIT and GPX files to Base camp.
  • FIT file name format "DD/MM/YYYY hh:mm:ss am/pm" (Start time)
    GPX file name format "YYYY-MM-DD hh:mm:ss" (End time)
  • FIT shows exaggerated total ascent. 799m.
    GPX shows correct total ascent.351m.
  • Open FIT file in basecamp. Properties shows individual record points.
    Delete any single line. Just 1. Any one. Then Total ascent shows correctly as 351.

This looks like a bug with the FIT file to me. Especially given it is fixed by deletion of any single point on the activity.

It is frustrating as it means if I use the 66S to record a hike the sync data in Garmin Connect is incorrect.

Any ideas?

  • Can you please email those fit and gpx files to me for inspection? 

  • I have sent you the files. Thanks.
    Try my test. Remove a single point from the FIT file and the total ascent will change.

  • Which firmware version is your device running? (Setup > About)

  • Latest version.

    Software version 6.00
    GPS SW Version 2.80

    Though I see the same discrepancy with earlier versions.

  • I am experiencing the same issue with total ascent value for my hikes. I have compared the value with other GPS devices I have carried with me (and my friends GPS devices) and the difference is way off, almost 2x. For a hike of 450ish m ascent my 66i reports an 850ish ascent :/. v 7.20 (gps 2.80, ciq: 3.0.12). my 64s reports the total ascent correctly in all cases.  

  • So I see 66S firmware 7.60 available today. No documentation about what it fixes as yet. I will test later.

  • For 66S not fixed in release 7.60. It is not listed as one of the fixes. But it was worth checking.

    Same symptom:
    FIT file has exaggerated distance and climb. GPX file correct.
    Open GPX file in basecamp - delete a single point. (Last one for example) - Total Distance and climb do not change.
    Open FIT file in basecamp - delete a single point. (Last one for example) - Total Distance and climb now match GPX. 

  • I have the same issue (with 7.20 and 7.60).

    I can provide more information (e.g. RINEX log, etc) if someone can/wants to investigation the problem.

    I'm trying to solve the problem with garmin product support without any success for more than a month - the support still can't figure out exactly what my problem is - I have the impression that for the support it is normal that the data is so inaccurate (x2 of the real ascent). In one of the messages they suggested me to turn on barometric pressure altimeter feature which started me to think that the support is actually a bot, not a real human - on my first message to them I described in detail that I tested different scenarios and the error happens with Barometer Mode: Variable Elevation and Altimeter Auto Calibration set to "Continuous" or "Once"... So shame on Garmin...