Why are all my runs now 1% Shorter than the 305???

So when I started running at home again after a week layoff, I started using my new Garmin 610 with the HRM.

The watch itself was great. The newer heart rate strap felt way better than the one that came with the 305, except that it seems to eat away at my skin where the monitor clips into the strap, but thats another problem...

First two runs were on a course that my 305 always measured as 5.21-5.22 miles. 610 measured 5.19 and 5.15. Getting a little concerned. 7 mile loop comes up as 6.95, OK not bad.

Notice the HR Alerts don't work on the watch when it comes out of sleep mode. Supposedly fixed in v2.20 firmware upgrade, I haven't tested it yet.

9.67 mile course measured as 9.58. OK, so the Garmin 610 measures about 1% less than 305 has been measuring for 3 straight years, I guess I can live with that.

Next run, after running for 30 seconds it said I had moved 0.01 miles and was running like 50:00min/mile pace. Mmmmm, maybe something is wrong at the start with this watch.

Same 9.57 mile course measured as 9.58. OK, still short. Seems to be a thing with the Garmin 610. 10.96 mile course measured as 10.86. Still,most people would tell me to shut up because, hey its within the 1% error tolerance that most people expect from their Garmin's, even though my Garmin 305 has measured the same distance for this course for 3 years.

The 9.67 mile course was measured in 9.56 one run, had me going 2 minutes/mile after my 7th mile. Never knew I was Usain Bolt. Start was off again, probably 20 seconds off for first mile.

A 7.3 mile loop is measured as 7.18. OK this is getting frustrating. Maybe its time to start looking at the GPX data this watch produces. Also, I should wear the 305 on a run at the same time.

OK, yesterday did a route that I have measure with tools online to be 12.53 miles. That my 305 consistently comes up as 12.48-12.52 miles for 3 years. Results: 12.52 miles for the 305 and 12.40 miles for the 610.

So I email Garmin Support and this is what they tell me:

Dear XXXXXXXX,

Thank you for contacting Garmin International.



I was concerned about possible GPS Drift. The time stamp appears to show the 305 started at .01 seconds ahead of the 610.

After collaboration with the engineers and sending your data to them the difference of .12 is within the acceptable ranges for GPS watches which is 1%. Also you may have had consistent readings with your 305 but they may have been consistently wrong and now you have a watch with correct readings the natural assumption would be that the 610 is wrong when in fact the issue may be with the 305.

I will be detailing in future posts all the errors I found in that run with the 610. I think there were at least 10 spots, probably 15 where the GPX data clearly shows a malfunction with the 610 GPS where as the 305 was nice and smooth.

And I guess I've been consistently running wrong for 3 years with my 305 on courses that it seems to exactly match. Ugh.