Accuracy of moving distance with Garmin VivoSmart

This is convenient device, but the question is how accurate the distance is?

Calculate distance based on steps

    I usually use Garmin VivoSmart for indoor training activities with a heart rate monitor.  I basically do not care so much for the distance I move.  I just need a profile of my heart rate during an exercise.  However, I just curious how accurate the distance on VivoSmart is.  So that I did an experiments to estimate the error amount on the distance.

Comparing with a distance on Treadmill

   Here is the method for this experiments.  Assuming the distance displayed on a treadmill is accurate enough, then I just checked a distance shown on the device and a distance on a treadmill after an exercise.  The result is that the actual distance shown on a treadmill is just 7.15km and the distance the device which is VivoSmart showed 11.43km.  The actual distance is about 63% of the distance the device shows.  So the distance on the device is about 1.5 times larger than the actual distance on the treadmill.  We could calibrate the distance to adjust a distance per step.  However I do not see much value to calibrate it because the distance per step can be different when a person is running and walking.  The distance per step is vary and I do not see much point to calibrate to get an accurate distance.  It is good enough for me to compare just relative distance each time.  I did this experiment a couple times and the distance and steps were consistent when we do an exercise with a similar pace and similar duration.

The device may count some even if a person is not moving …..

   The other thing I found was the device could count steps even if a person is not moving, such as during driving, typing and playing a piano, I do see the number of steps keep increasing.  If a person who does not do much exercise, then the error amount could be larger.   On the other hand, if people who do more exercise, it is not a big deal.  Since the percentage of such false counting is smaller than actual moving distance.  In my case, I usually move more than 10,000 steps and it is not a big problem at all.  As a conclusion, I think number of steps is reasonably accurate and as long as people understand the limitation, it should not be bad.  I think the distance with some calibration would be accurate enough.  However people who really want to get accurate moving distance in outdoor, I suggest to get a device with GPS function.