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Various questions need to be addressed.... Are you certain the distance is accurately measured if so by whom and was it certified.How far out is your garmin and does it not tell you how accurate it is? -- my 310xt displays its degree of error.
Are we talking have a mile out of are we talking a couple of feet
There are two issues. The first is how far you actually ran. Even on an accurately measured course there is a small margin of error. They always err too long. Then they measure the shortest racing line but it's unlikely that you will run that line.
Secondly, the way the Garmin measures distance is by checking your location periodically. It then works out the distance from the last time it checked your location. It does this in a straight line and if you didn't run a straight line betwen those points is will be inaccurate. The more frequently it checks your location the more accurate it will be. If it loses the satellite signal then it simply takes a straight line from where the signal was lost to where it is regained.
That's why your Garmin is unlikely to ever show exactly 10k on a 10k race.
Every race will be a slightly different length and officially measured races alway add on a certain percentage to ensure they are not short (so in effect every race you do should be long on your Garmin if its officially measured). Actually distances can vary quite significantly to the extent where certain races are known to be good or bad for PB potential given their actual length. As an example I ran 2 10ks in the space of a few days last year both on officially measured courses. My Garmin recorded my pace as identical for each run but my finishing time differed by about 40 seconds.
As has been said the more twists and turns and changes of direction the less accurate the Garmin readings will be. As an aside there is usually a setting which you can change which alters how often the Garmin takes readings. You can set it to take them more often which gives greater accuracy but uses up more of the memory.
Mine (405) is usually pretty damn close to the measured course distance.
On the other hand, my OH's 305 always says more distance has been covered.
I certainly consider my 405 to as accurate as I need for training, etc.
Kicked-It wrote (see)
Just wondering how anyone could comment on the accuracy of the HRM without access to hi-tech specialist medical equipment?
Mr Viper wrote (see)
As an aside there is usually a setting which you can change which alters how often the Garmin takes readings. You can set it to take them more often which gives greater accuracy but uses up more of the memory.
Could you please indicate how could we view/edit the settings
MandM wrote (see)
Mr Viper wrote (see)
I agree that its quite accurate but thats probably true for straight line runs, i believe the deviation comes when you have a lot of twist and turn in your run, i was down by 400 yards on a 20 Miler, but i knew that cos the run involved lot of of twist & turn and some loops!
I guess no harm knowing that you could improve distance logging and get greater accuracy.
My 305 measures pretty much the same as when I used Mapometer.com. Im not sure how accurate the HRM is though. When I set off and I am on a warm up lap it seems to make my HR around 237 which just cant be correct. It does settle after a while and seems to give a more realistic reading.